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.