Tarantula Hawks

I consider wasps my favorite insects. The honest truth is that I first took interest in them because nobody could call me a sissy for collecting an insect that could fight back! The more I learned, though, the more fascinated I became with their behaviors and sheer diversity. The solitary “spider wasps” of the family Pompilidae are one such example.

Here in Arizona, spider wasps reach the gargantuan proportions of the so-called “tarantula hawks” in the genera Pepsis and Hemipepsis. The largest females exceed two inches in body length. The standard appearance of these colorful insects is an iridescent blue-black body with bright orange wings, though some species have black wings with bluish reflections.

Thankfully, despite their size and high voltage sting, the females are generally placid, not easily aroused as they seek nectar at flowers. Milkweed is decidedly their favorite source of nectar, but I have also seen them on blooming creosote bush (as this female Pepsis chrysothemis demonstrates), blue palo verde, eucalyptus, and various mesquites and acacias. Females will also drink water at the edges of puddles and ponds.

Males are often more numerous at nectar sources than the females, and are recognized by slimmer bodies, longer antennae, and long, flattened hind legs. The males can also gather in multi-species “bachelor parties” during the hottest hours of the day, and also overnight and during inclement weather. They gather on certain trees in large, loose clusters. The odd female may join them, though mating does not seem to take place at such congregations. The males of at least some species perform a behavior called “hill-topping,” whereby they perch on trees at the highest point in the surrounding landscape, the better to spot and intercept passing females as they fly below.

Once mated, the females go about the business of earning their name. They search feverishly on foot, with flickering wings and quivering antennae, for the burrow of a tarantula spider. This behavior frequently takes place in the cooler morning, evening, or overnight hours, and is not often observed.

An occupied burrow discovered by the wasp usually results in the spider chasing the wasp back aboveground, and the battle is on. Initially it is a series of strategic maneuvers, each animal well aware of the agility and weapons the opponent possesses. Most of the time the female wasp manages to eventually sting the spider on its underside, striking a nerve center that renders the hairy arachnid paralyzed. She then sets about dragging the helpless victim to the nearest underground cavity, often choosing the spider’s own burrow. The tarantula hawk then lays a single egg on the still-living but comatose spider. The larva that hatches will then consume the spider as it grows ever larger during the long feast. The grub eventually pupates, and emerges as an adult wasp months later. Given the abundance of the wasps, there must be a very large tarantula population in the Sonoran Desert.

Tarantula hawks are diverse, too. I have personally collected seven species in Tucson alone: Hemipepsis ustulata, Pepsis grossa, P. chrysothemis, P. mexicana, P. thisbe, P. cerberus, and P. mildei.

My good friend Justin Schmidt, an outstanding research scientist, ranks tarantula hawks near the top of his “sting scale,” but has learned something very interesting. He concludes, both from personal experience and chemical analysis, that the venom of these wasps causes excruciating, short-term pain in humans (and likely other mammals), but does virtually no damage to tissues, nerves, or any bodily functions. You are in utter agony for about three minutes, and then you generally can resume normal activity.

Personally, I think it pays to heed the bright aposematic (“warning”) colors of these wasps, and to let them be. I’ve also learned that, once in my net, the wasps adopt a threatening posture with wings flared and abdomen curled, while liberating a distinctive fragrance at the same time.

My own fascination with these wasps only continues to grow, and I encourage everyone who encounters tarantula hawks to react calmly and enjoy watching them live out their lives. After all, few insects are so large and colorful.

Tucson Grasshopper Story on TV

This afternoon I was privileged to be interviewed by Delane Cleveland, a reporter for FOX News 11 at 9 regarding a sudden increase in the local grasshopper population. The insect in question is the Pallid-winged Grasshopper, Trimerotropis pallidipennis, normally quite abundant as it is, but occurring now in numbers that can be disturbing to some people. It pays to put this population boom in perspective, however, and to let people know of easy ways to deal with them while they are here.

The Pallid-winged Grasshopper is a member of the family Acrididae, or “short-horned grasshoppers,” named for the short antennae (in contrast to katydids and crickets which have very long antennae). While some members of this family have a truly migratory phase called a “locust,” this species flies shorter distances in vastly smaller numbers.

Locusts represent an actual physiological change in the body of a normally solitary species, triggered by crowding to the degree that the young (nymph) insects are literally rubbing elbows with each other. This physical contact causes them to not only become more gregarious, but leads to a sleeker, longer-winged adult than usual. Nymphs of locusts will march in armies, devouring nearly every green piece of vegetation available. As they grow, eventually molting into adults, they retain their social nature. Pushed by strong storm fronts, they fly hundreds of miles, continuing to lay waste to the landscape.

There is historical documentation of infrequent outbreaks of the Pallid-winged Grasshopper, much more severe than we are seeing currently, that were problematic in rural, agricultural areas in Arizona. This year’s population represents a mere nuisance by comparison.

Should you still worry, what do you do? Pallid-winged Grasshoppers feed primarily on grasses, but will also eat some herbaceous vegetation (called “forbs”), so homeowners may wish to cover such vulnerable plants in the garden during the grasshoppers’ layover. Also, the grasshoppers are attracted to lights in droves during the overnight hours. Simply turning off outdoor lighting will help to decrease their numbers, at least in your own private yard. Consider wearing sunglasses, as some errant ‘hoppers, disturbed by your footsteps, may fly up in your face. Please avoid the use of chemical controls, as those poisons can be harmful to the natural predators of grasshoppers, such as spiders, birds, and lizards. Remember, such population increases are temporary, a fleeting blip in nature’s seasonal time frame.

My compliments to Mr. Cleveland and his videographer for producing a fine story, free of the sensationalism that the media often adds to such natural phenomenon. Stay tuned for more on grasshoppers, and other insects you are likely to encounter throughout the year.

Earth Day Bugging You?

We might as well refer to “Earth Day” as “Bug Day.” Insects, arachnids, and other arthropods account for over 80% of the planet’s biodiversity and biomass. They are the foundation of many food chains, the decomposers of the dead, pollinators of plants, agents of seed dispersal, and the subjects of important scientific research. No, despite all of this, we still gravitate to cute and cuddly vertebrates, the “charismatic megafauna,” as symbols for Earth Day.

We collectively tend to think of insects as organisms that will lay claim to the planet once humans have left it beyond repair, but the truth is that many insects are just as vulnerable as vertebrates to environmental degradation. State and federal lists of threatened and endangered species often include insects and other invertebrates among their ranks. Many of those are inhabitants of freshwater, cave, or dune ecosystems, among the most fragile of habitats.

While it has been difficult to gain protection even for vertebrates, endangered insects and their kin are often viewed as impediments to economic development and prosperity. “Bugs” clearly need an agent experienced in public relations and spin control. Maybe even a pitch man. Hey, where is Billy Mays when we really need him?

Earth Day would be the perfect stage for promoting insects and other arthropods as the support network for our planet. Further, as I often say, “biodiversity begins at home.” What better way to drive home that point than by lobbying to curtail the use of do-it-yourself pesticide chemicals and treatments? You would kill two birds with one stone (or possibly let two birds live by eliminating a source of environmental contamination, and promoting a healthy balance of predator and prey in the home and garden).

Entomologists, science writers, and media professionals all need to do a better job of broadcasting the fundamental truths about what arthropods mean to nature and humanity. We have been too timid, too remiss, too wrapped up in research and writing about topics that we think we can “sell” to editors, publishers, and radio and television executives. It is time for a change, and we can make it happen. Yes, we can.

For another take on Earth Day, please see Sense of Misplaced. Thank you.

Desert Grasshoppers

Grasshoppers are some of my favorite subjects to photograph. You can creep close to them without spooking them, so confident are they in their camouflage. They are basically two-dimensional, so it is easy to get a lateral view of them with everything in focus. Lastly, they are common insects.

Most diurnal grasshoppers belong to the family Acrididae, known as “short-horned grasshoppers” for their short antennae. Few species in North America are of economic consequence, so it is easy to ignore them, but you would be missing a subtle beauty if you passed them by.

Take the “cream grasshopper,” Cibolacris parviceps, for example. They appear to be little (20-32 mm) flying bits of granite. Ok, when they are young, without fully-developed wings, they resemble hopping bits of stone. This species ranges throughout the southwest, occupying such desolate habitats as dry desert washes (arroyos), overgrazed rangeland, and, in some parts of Tucson anyway, unpaved parking lots. Initially, I thought this insect was one of the colorful band-winged grasshoppers in the subfamily Oedipodinae, but I was mistaken. So, apparently, were early taxonomists who did classify the genus there. Today, most orthopterists (grasshopper experts) put Cibolacris in the subfamily Gomphocerinae, known as “slant-faced grasshoppers.” The rationale for that escapes me.

A true slant-faced grasshopper is Psoloessa texana. This diminutive (16-22 mm) creature is very cryptic among plant debris, owing to the complex patterns of lines, diamonds, and spots on its body.

The most common of our local grasshoppers by far is the Pallid-winged grasshopper, Trimerotropis pallidipennis. It is abundant in vacant lots, even on city streets where they may bask in the morning. They are true band-winged grasshoppers, the pale hindwing, used in flying, marked with a broad black band. These wings are concealed, folded accordion-like, beneath the narrow, mottled forewings when the insect settles, rendering it nearly invisible. That is quite a vanishing act for a sizable (31-42 mm) insect. This wide-ranging species occurs from western Canada to Chile.

While the pallid-winged grasshopper can fly very far, very well, most winged grasshoppers fly very short distances before settling again. This is true for the Aztec Range Grasshopper, Lactista aztecus, also out and about now in Tucson. This small (19-25 mm) insect has yellow hindwings interrupted by a black band. The single bar across the forewing (matched by a bar on the femur of the hind leg) makes it easy to identify. It ranges from Arizona to Texas, south into Mexico.

Wherever you live, there should be grasshoppers. Take a closer look at them and see if you, too, aren’t delighted by their earthtone colors and captivating personalities as you play hide-and-seek with each other. Share your stories and discoveries here, and/or post your images over at Bug Guide where others can enjoy them as well.