Professor Steven Goldsmith

Tarantulas and Tarantula Hawks

You may think I am crazy about predators and parasitoids, but I am not, particularly. I just think they are cool and important parts of their ecosystems. The way parasitoids make their living is unusual, but there is actually a pretty fair number of these species. Flies of the family Tachinidae are parasitoids, as are essentially all members of the wasp families Ichneumonidae (about 60,000 described species) and Braconidae (12,000 described species, with estimates of 50,000 to 150,000 species total). The subject of this post is the family Pompilidae (spider wasps), which includes a group of species referred to as tarantula hawks (genera Pepsis and Hemipepsis).

Tarantulas are obviously large, relatively primitive spiders. The terrestrial species (which we have in north Texas, and for that matter throughout North America) live in burrows in the ground, which they line with spun silk. Tarantulas themselves are predators, and capture crickets and other small arthropods, although some of the larger species in the Neotropics can capture small vertebrates. The tarantulas in the US are essentially harmless to people (although they can be scary) - they can be picked up and handled carefully; some species are kept as pets. One of my office mates in graduate school had one that he kept in our office, and he would occasionally take it out of its terrarium and let it walk around on his arms. There is not much in biology that gives me the willies, but that did.

Tarantula hawks are often relatively large wasps (up to 2 inches), heavy-bodied, with dark bodies and smoky, reddish-orange wings. Tarantula hawks are called that because the females hunt tarantulas to provide for their larvae. You will see them flying slowly a couple of feet above the ground surface, in a pattern that almost seems methodical. They probably find tarantulas using vision more than hearing or smell - it is not uncommon to find tarantulas out and about during the day, although they are primarily nocturnal. When a tarantula hawk finds a tarantula, it stings it to paralyze the tarantula, in much the same way that cicada killers paralyze cicadas.

The tarantula hawk next drags the tarantula to a burrow. There are conflicting reports about this - some say the tarantula hawk digs a burrow in which to place the tarantula, others say the tarantula hawk places the tarantula into the tarantula’s own burrow, which would seem to be the height of adding insult to injury. My guess is that, as Forrest Gump says, it is probably some of both - an individual tarantula hawk probably sometimes digs a burrow, and sometimes uses the tarantula’s burrow.

The tarantula hawk (females only) lays an egg on the body of the tarantula. The egg hatches into a larva, which bores into the tarantula’s body, consuming the internal organs, eventually killing the tarantula and pupating. The pupa ecloses as an adult wasp, starting the life cycle over.

 

Allergy season

In north Texas, we are far enough from the ocean to have four distinct seasons, and we are far enough south that we generally have long, hot summers and short, mild winters, and usually enough pleasant weather in spring and fall that we can open up the house for days, even weeks at a time.

Unfortunately, we also have four allergy seasons. Late summer and fall is ragweed pollen season - more on that later. Winter is mountain cedar pollen season (more appropriately known as Ashe Juniper because it is not a cedar and is not restricted to mountains) - I am particularly allergic to this one. Spring is grass/tree pollen season, with a medley of pollen in the air. Summer is fungus spore season. We are right in the middle of that. The “pollen count” in Dallas has been running at least 7000 grains/cubic meter of air, and is nearly 9000 grains/cubic meter today (with a little ragweed mixed in for good measure). Even during other allergy seasons here, there is a chronic background level of fungus spores that is often greater that the levels of other pollen.

One of the worst offenders among the spore-producing fungi is the puffball. There are several species of puffball-producing fungi in North America, many of which are in the genus Calvatia. The puffballs we have in this part of north Texas are mostly Calvatia cyathiformis - this specific epithet refers to the cup-like morphology of the puffball.

An individual puffball may release trillions of very tiny spores during the few weeks that it is “active” above ground. Release of spores from puffballs is triggered by mechanical stimuli (wind, raindrops, people poking them with sticks, etc). The spores of C. cyathiformis seem to be particularly allergenic - I don’t know whether that is because of their spiky surface of some chemical characteristic. Once the puffball is spent, it deteriorates.

(scanning electron micrograph of C. cyathiformis spores; image from http://www.nemf.org/files/sam/Spores/sporeshow/fv19.htm)

Puffballs, mushrooms, and shelf (AKA bracket) fungi are the sex organs of various species of fungi within the fungal taxon Basidiomycetes.

(a "chicken mushroom")

(a "fairy ring" of mushrooms)

(a "bracket fungus")

The body of the fungus (the mycelium) is under the ground. The mycelium of large fungi may cover many square feet and weigh many kilograms. In fact, mycologists claim that the largest living organism (and potentially the oldest) is a fungus. This seems even stranger when you know how the body of a fungus is constructed. The mycelium comprises a large number of very small tubes called hyphae. Hyphae have an outer covering of chitin that is semipermeable, and they contain cytoplasm, organelles, and nuclei, like "normal" eukaryotic cells. The hyphae branch and anastomose, and form a dense mat, but they are still just very small tubes (2-10 microns, much finer than a human hair).

This is an alien way to structure the body of an organism, but it works for the fungi. Fungi make their living by being “absorptive heterotrophs,” which means they are not photosynthetic (autotrophic), but instead take up organic material from the environment by first secreting enzymes to digest the material, then absorbing it into the hyphae. Having a body composed of a huge number of fine tubes increases astronomically the surface area for secretion and absorption.

Fungal reproduction, at least within the Basidiomycetes, is a bizarre affair. The spores produced by puffballs and their ilk are “haploid,” having only one of two sets of chromosomes, and being produced by the cellular process of meiosis. The spores are akin to sperm and eggs produced by humans and most other vertebrates. The spores germinate to form hyphae, and the hyphae grow into what is called a primary mycelium. Each primary mycelium is either “female” or “male” (mycolgists don’t use these familiar terms, but the gist of it is the same).

If a female primary mycelium encounters a male primary mycelium, they coalesce to form a secondary mycelium. You would think, at this point, that the female haploid nuclei would join with the male haploid nuclei, like a sperm joining with an egg to form a diploid individual. But NO, the fungi don’t do it this way. They keep their haploid nuclei separate but living in the same body, sometimes for years, until it is time to make new spores. Then the secondary mycelium produces basidiocarps (the puffballs, mushrooms, and bracket fungi that are the genitalia of the fungus). Within these structures the nuclei come together to form diploid nuclei (the process is called karyogamy), then immediately undergo meiosis to form haploid spores. These are the spores that cause so much misery among allergic humans. Bizarre!

 This cartoon will illustrate:

 

 

Robber fly and grasshopper

A few days ago I went out to get in my pickup truck to run some errands, and I noticed something unusual on the radio antenna. I looked more closely, and saw that a robber fly (family Asilidae) had captured a grasshopper (almost certainly family Acrididae).  The three pairs of legs of the robber fly are pretty visible because they are red and black - the first pair is holding onto the antenna, and the middle and back pairs are holding the grasshopper, which is sort of twisted and mangled - the abdomen of the grasshopper twists to the grasshopper’s left where the end of it is being held by the robber fly’s back legs. The grasshopper’s wings and legs are sticking out at unnatural angles. It is not clear from the image, but the robber fly’s mouthparts are almost certainly inserted into the grasshopper’s thorax.

The robber fly has a “piercing and sucking” type of mouthpart, which entomologists call “haustellate.” You know that insects with haustellate mouthparts can deliver a painful bite if you have ever been bitten by a horsefly or an assassin bug.

(the "wheel bug," a member of the assassin bug family {Reduviidae} - the haustellate mouthparts are visible just to the right of the base of the antennae)

Haustellate mouthparts form a tubular, hypodermic syringe-like structure, which suck body fluids out of the prey, but can also deliver salivary secretions (anesthetics, anticoagulants), as in mosquitoes and kissing bugs.

When most people think of predators, they think of lions, tigers, bears, or great white sharks (especially in western Australia). Most people don’t think of small animals being effective predators. But here you can see a small insect (not more than an inch in total body length) actively consuming another insect that is probably longer and more massive than the predator that is eating it. Predators of any size are important parts of the economy of nature.

For a scientist, an observation like this leads to many questions that do not have obvious answers. How did the robber fly manage to capture the grasshopper? How did it locate it in the first place? How did the robber fly carry the grasshopper from where it captured it to the antenna of my pickup truck? How often does a robber fly need to capture a grasshopper to sustain itself? Are robber flies opportunistic, or are they selective about the grasshoppers they capture? Do robber flies capture prey other than grasshoppers?

I have some evidence that robber flies do capture prey other than grasshoppers. I took the photo below several years ago at Hagerman National Wildlife Refuge. This is a different species of robber fly, and you can see that it has captured a housefly (the housefly’s eyes and wings are visible below the eyes of the robber fly). 

 

The Family Asilidae is a large one, with about 1000 species in North America. The adults feed on a variety of insect prey, including grasshoppers, other flies, bees, wasps, and dragonflies. They typically capture their prey on the wing, and as we saw above, often capture prey as large as themselves or larger. Obviously they are powerful and agile fliers. Vision is their primary sensory modality in predation; note the large, bulging compound eyes. In many habitats, robber flies are numerous - watch for them in your neighborhood!

 

Korean Barbecued Chicken

This blog is mostly about biology, but because biology is about organisms, and because the ultimate fate of all living organisms is to become food for other living organisms (or to be dissipated as heat back to the environment), sometimes this blog is about food. This is one of those times. If you want to go right to the recipe without reading the back-story, scroll down to the end of the post.

It is probably odd that as a biologist in Texas, I have spent more time in Hawaii than in any other state that I haven't lived in (those are Missouri, Oklahoma, Arizona, and Texas). This is because of my January Term course, Natural History of the Hawaiian Islands

(the 2006 group in Haleakala crater - they are smiling because they don't realize that they have the last third of a 12-mile hike, with about 2000 feet elevation gain, to get to the vehicles)

and because of my research project on longhorned beetles (Plagithmysus) at Hakalau Forest National Wildlife Refuge.

(a view down the "Alley" with koa plantations on the right and makai)

Between January Term and research I have spent the better part of a year in Hawaii over the past 12 years or so. Most of that time has been at HFNWR, but a close second is Hilo, on the windward side of the Big Island. Hilo is a small but interesting city, with substantial ethnic diversity and a population that includes many native Hawaiians. The ethnic diversity includes Japanese, Chinese, Filipinos, Portuguese, your standard haole, and importantly for this post, Koreans.

(Hilo in the morning from Moku Ola - Coconut Island)

For the first several years that I visited Hilo, there was a small, literally hole-in-the-wal Korean restaurant in a primitive strip mall at the corner of Kawili Street and Manono Street. I went there for lunch at least once during each of my first several visits. The dish that I always ordered was, you guessed it, the Korean barbecued chicken. The chicken was marinated, slow grilled, spicy but sweet, and very flavorful. The chicken was served with steamed rice and pickled vegetables.

There was some point, I am not sure when, that I was in Hilo, and the restaurant was closed. I was back in Hilo a couple of weeks later (having spent time at the refuge), and the restaurant was still closed. There was an older local woman there when I was there, and I asked about the restaurant, and she said, “I think they are gone for good.”

I thought, bother, where am I going to get Korean barbecued chicken? I decided I would have to invent a recipe and do it myself. It may seem odd, but my first try nailed it.

Korean Barbecued Chicken:

Marinade chicken in a mixture of:

• black vinegar (1/4 cup)
• brown sugar (1/8 cup)
• chili paste (1/8 cup)
• garlic (2-3 cloves, pressed)
• sesame oil (1 tablespoon)
• tamari (1/4 cup)

How much of these you use depends on how much chicken you are going to cook. I generally don’t measure the ingredients, but it tends to turn out about the same each time anyway. I usually use a mixture of chicken breasts (boneless, skinless) and thighs (also boneless, skinless) – I usually cut the breasts into two or three pieces before marinating. The amounts above are about right for 3-4 breasts and 6 thighs (which are the amounts in a package of breasts and a package of thighs from Wal-mart), which is enough to feed the houseful of folks that I usually cook this for (6 adults and two grandchildren). Marinade overnight or longer (longer is better, up to 4-5 days). Grill over low heat for 40 minutes or so – spray grill surface with Pam before cooking. Watch the chicken while it is cooking, because the brown sugar tends to make it stick and burn. When you turn the chicken over, pour any leftover marinade over it. Turn the chicken over and move the pieces around to get it to cook evenly. Watch it more closely on a charcoal grill than on a gas grill.

Serve with Korean rice, sticky rice, or cheese grits. Kim Chee goes well also, and caramelized onions. Becky always has to have a salad and a green vegetable.

I might post the recipes for Kim Chee and cheese grits later. Stay tuned.

       

Summer in north Texas

You know high summer has arrived in north Texas (and many other parts of the country) when the cicadas start buzzing. These large insects have an interesting life style and life cycle. The last-instar nymphs emerge from the soil beginning in early July, and eclose from their final nymphal exoskeleton to become adults.

 

The adults take to the trees, and the males begin their incessant calling for mates. The calls can be so loud and numerous as to be deafening. Females find and choose males based on their calls, mate, and lay eggs on the twigs and small branches of trees. The eggs hatch into tiny nymphs, which girdle the twigs, killing them, then drop to the ground and burrow into the soil. The nymphs feed on the sap of tree roots using their piercing and sucking (“haustellate”) mouthparts. Around here we have “dog day” cicadas, whose nymphs live and grow for 5 to 7 years before emerging to begin the cycle again.

Another signal that high summer has arrived is the appearance of the cicada killer wasp (Sphecius speciosus). This species is a “parasitoid,” which means that it is not exactly a parasite, but also not a predator in the way we normally think of predators. The mother wasp locates a cicada by listening for the cicada's call, then stings the cicada to paralyze it, places it into a burrow, and lays an egg on it.

 

The egg hatches into a larva, which bores into the cicada and feeds on the internal organs, saving the vital organs for last. The wasp larva kills the cicada, and pupates within the cicada’s exoskeleton. After about a year, the pupa ecloses as an adult wasp, and begins the cycle again.

Cicada killer wasps can be quite numerous in places where the soil is good for burrowing. The females prefer sandy soils in places that are near trees that harbor cicadas. The female wasp in the image above had dug her burrow in the sandy soils beneath a wooden deck in our backyard in Sherman. The wasp could fit between the deck boards, but the cicadas were too large to fit, so the mother wasp had several of them lined up because she couldn’t get them down into her burrow. I got out my hand-held jigsaw and widened the gap a bit. I came back later and all of the cicadas were gone, presumably down into the wasp’s burrow. I like to help the predators out when I can, because they are an important part of the economy of nature.

 

Mount Davis, PA

I recently had the opportunity to visit Juniata College in Huntingdon, PA. Juniata is a small liberal arts college, in many ways like Austin College. Huntingdon is a pleasant small town in rural central Pennsylvania. It is not easy to get to Huntingdon - it is considerably more off the beaten track than Sherman, TX.

After my visit to Juniata, I made my way from Huntingdon south and west toward Somerset County, the location of the highest point in Pennsylvania, Mount Davis. This part of Pennsylvania is rolling hills with woodlots and tidy, well-kept farms.

 

Mount Davis is 3213 feet above sea level. It is simply the highest point along a long northeast-southwest trending ridge. The climb to the summit of Mount Davis is neither a long nor a strenuous walk. In fact you can drive to within a very short walk of the actual summit. I parked at the Mount Davis picnic area and “climbed” about a mile along a fairly well maintained trail. There was not much elevation gain, and it took me about a quarter hour to make the “ascent.” The summit area had some plaques attached to boulders that described the history, geography, and geology of the area.

 

 There was a trail map as well. The trail map showed an alternative route down to the picnic area that went past the “sheltered rocks.” I thought I would take that route on the way down. I took some photos of the summit area, then I started down the short trail to the parking lot - I wanted to see whether there were any other folks at the summit - there were not. Not far along the trail to the parking area, I noticed movement on the trail just ahead - there was a nearly two-meter Timber Rattlesnake (Crotalus horridus) leisurely crossing the trail. I have seen many venomous snakes in the wild, so it did not spook me.

 

A bit later, I started down the Sheltered Rocks trail, which would take me back to the picnic area in about 2.25 miles. I hadn’t gotten far when I thought, OK, I am here alone, there is no cell phone coverage, I am already a mile from my vehicle, and I just saw a large venomous snake. I backtracked to the parking area and walked down the road (not the trail) back to the picnic area. When I got to the picnic area, a Pennsylvania State Forest service truck passed me, pulling a large green metal cylinder on wheels. As it passed, the words “DANGER - BEAR TRAP” were clearly painted on the sides. I was glad I had seen only the rattlesnake and no bears.