More Hilltopping Insects

I finally got the full effect of a hilltopping experience on March 25 when I hiked to the summit of Sentinel Peak (“A” Mountain), just west of downtown Tucson, Arizona. At only 2, 897 ft. (883 meters) above sea level, and rising a mere 522 feet off the desert floor, it is more of a butte than a mountain. Still, its relative isolation makes it an effective magnet for hilltopping insects.

“A” Mountain is named for the immense concrete letter on its eastern slope, painted in the red, white, and blue colors of the University of Arizona. Most folks visit the top for the spectacular panoramic view of Tucson and its surrounding mountain ranges. It can be a romantic setting at dusk, too. Male insects of many species come there for romance as well, but usually have to defend territories or otherwise repel rival males in the process.

Among those insects are bumble bee-sized bot flies, Cuterebra austeni. The big, black and white adults are not often seen during their brief existence. They have no functional mouthparts and are fueled only by burning the fat reserves they accumulated in the larval stage. As larvae they are subdermal parasites of either rodents or rabbits, depending on the species. I’ll spare you the gory details.

The male flies conserve their energy and will allow you to approach extremely closely if you do so carefully. Once startled, or when they detect a rival or a female, they jet off at warp speed. Eventually they return to the same spot, or very close by.

A more typical, larger, and colorful hilltopping insect is the black swallowtail, Papilio polyxenes. These butterflies are in seemingly constant motion, flying swiftly across the summit and only pausing to perch for very brief periods.

They are incredibly aggressive, chasing each other mercilessly. You can actually hear their wings and bodies colliding, so violent are their aerial duels.

Perhaps the most unexpected and unusual insect I discovered was the pollen wasp Pseudomasaris maculifrons. Pollen wasps are solitary insects in the same family as potter wasps, mason wasps, and the social hornets, yellowjackets, and paper wasps. While her cousins feed their larval offspring with other insects, the female pollen wasp stores pollen and nectar in her mud nest.

Males are easily recognized by their peculiar antennae: long and clubbed. Females have much shorter, clubbed antennae. Males of this particular species are known to perch repeatedly in the same small area, day after day, for as long as 29 days (Alcock, John. 1985. “Hilltopping Behavior in the Wasp Pseudomasaris maculifrons(Fox),” Journal of the Kansas Entomological Society, 58(1), pp 162-166). Between February and May, different generations of males occupy the same locations in different years. They are very active insects, but do not appear to be nearly as belligerent as bot flies or black swallowtails.

It turns out the top of the peak also attracts other insect photographers. I crossed paths there with my friend Philip Kline, who I hadn’t seen in probably two years! We had a great time catching up, and helping each other identify the insects we were seeing.

May your own hilltop experiences be just as rewarding and enjoyable. You could very well discover something new (especially regarding bot flies), to yourself or the scientific world.

Sometimes you become the best perch on the peak!

Hilltopping

One of the more interesting types of insect behavior is something called “hilltopping.” While hiking along a ridge in Tucson Mountain Park on Friday, March 5, I witnessed this firsthand.

Hilltopping describes the mating strategy of male insects of some species that will fly to the highest point in their immediate landscape. This may be a mountain, a butte, or even a small hill, provided it is sufficiently elevated above the surrounding terrain.

Once at the summit, the insects pursue one of several courses of action. Males of some species will defend a small territory such as a perch on a boulder, shrub or tree that affords the best view for spotting approaching females of the species. Competing males will be driven off. Butterflies in the family Lycaenidae, such as the Great Purple Hairstreak, Atlides halesus, and the Gray Hairstreak, Strymon melinus, both pictured below, defend perches.

Another method employed by males is “lekking,” in which several males congregate in an area where they display to females. Females then choose what they perceive as the fittest male specimen and mate with him. A “lek” is the term for the “stage” on which the males “perform.”

Still another form of hilltopping is when a male “patrols” a route along the summit of a hill or ridge, hoping to intercept a passing female. Many butterflies in the family Pieridae exhibit this behavior, also known as “scramble competition polygeny.” Males don’t have territories, but will actively compete when two of them spy the same female. The battle may consist of spectacular vertical flights, the two males spiraling around each other until one ceases to ascend further, conceding defeat. On my own hike, I noticed several males of the Desert Orangetip, Anthocharis cethura patrolling along the ridge, together with what I believe were Sleepy Orange butterflies, Eurema nicippe. Also seen at the summit of the ridge was a male West Coast Lady, Vanessa annabella, that repeatedly returned to the same patch of ground.

Besides butterflies, major hilltopping insects include several species of Hymenoptera (bees, wasps, ants) and Diptera (true flies). Flesh flies in the family Sarcophagidae, such as the one pictured below, were present on my afternoon sojourn.

To see the most variety of species, I would recommend spending all day at the very top of a likely hill, ridge, or mountain. The fauna will change as the hours pass and conditions change. Here in the desert at least, some species hilltop for only a few hours in the morning, then disappear. Other species are present all day, or may be most active in the afternoon.

Especially at this time of year, early spring, hilltops may be the only places to find an abundance of insects. Not only will you see hilltopping species, but other species that come to prey on them. I’m sure that is the only reason that dragonfly was up there, perching on a cactus of all things.

NOTE: I highly recommend reading the works of Dr. John Alcock for more about hilltopping insects. His books include Sonoran Desert Spring and Sonoran Desert Summer, both being collections of outstanding literary essays.

"Bee-Bop"

When photographing normally active, fast-moving insects like bees, it often pays to catch them when they pause to groom themselves. On March 1, while retrieving the mail, I discovered this exhausted worker honeybee on the steps of my apartment building. She gave me a great opportunity to get some nice close-ups while she cleaned herself.

Another advantage to shooting images of grooming insects is that the creature often displays features of its anatomy not normally visible when it is simply resting, or going about its regular business of pollinating, eating, mating, or transporting itself. For example, a bee’s abdomen is usually concealed by the wings folded over its back at rest. As she shifted her weight to allow her to rub her hind legs together, this worker revealed her abdominal pattern.

The little dance she was doing was cute and amusing to me, but all business to her. Bees, both social and solitary, easily become gummed up in residual nectar and other floral exudates, or damp soil that adheres to their bodies in the course of excavating a nest burrow. “Setae,” the sensitive body hairs that aid a bee in navigating its environment, must be kept free of such debris in order to function properly.

It might look here like the bee is insulting me by sticking out its “tongue,” but her mouthparts need to be kept clean as well. While bees have chewing mouthparts, they also have highly modified segments, some of them fused into a tongue-like appendage that lets them lap up nectar.

This bee eventually re-energized, and redeemed herself by giving me a respectful salute before flying off to resume pollinating flowers and/or scouting for a new nest site.

Carpet Cocoon

One day after I discovered the ”Carpet Caterpillar,” I discovered the remains of its cocoon in my living room carpet. This also explains why the caterpillar was so lethargic when I found it: a great amount of energy is expended in preparing to pupate.

Actually, there were the remains of two cocoons. Since I did not find another caterpillar, I suspect that I disrupted the one animal on two occasions. I was using boxes that had been in that spot for ages, and the caterpillar, once exposed, probably sought refuge under another box that I also eventually used.

You can even see the “trail” between the two pupal cells, a tiny trough in the carpet. Whether this represents actual damage to the fibers I have yet to find out (hey, I’m blogging, not vacuuming).

Another Honor

Last week I discovered that I was one of the top fifty (50) experts at AllExperts.com for the year 2009. Not that About.com, the parent of AllExperts, bothered to tell me or anything. Still, I'm flattered.

The ranking is probably based on the scores given to the expert by satisfied users of this "aska service," divided by the number of questions you answer. Considering the number of doctors, lawyers, and information technology wizards that must entertain thousands of questions each year, I'm proud to help elevate entomology to this level of prominence. Keep the questions coming, folks.