The BugLady stumbled across these very different beetles while on the trails at the Bog and Riverede this summer.
The ANTELOPE BEETLE (Dorcus parallelus) is a hefty (inch-long) beetle that certainly does not make one think of antelopes. It’s in the stag beetle family Lucanidae; males in this family tend to be bulkier than females and often come equipped with formidable mandibles, with which they fight over the ladies. Male Antelope beetles have an upward-pointing spur on each mandible http://bugguide.net/node/view/309163/bgimage http://bugguide.net/node/view/281091/bgimage and the BugLady is guessing that its name comes from the resemblance of their mandibles to the horns of the American Pronghorn (a.k.a. Pronghorn antelope, though it’s not in the true antelope family).
There are two species in the genus Dorcus north of the Rio Grande (most of the 30 or so species live in Asia) – D. parallalus and D. brevis, which was originally lumped with D. parallelus. As always, there is some variation/overlap in size and shape within each species, and although their classification seems settled now, their identities were the source of an occasional entomological “dust-up” in the early days. A note in the Proceedings of the Entomological Section, Academy of Natural Sciences, Philadelphia (April, 1892) (an organization that was co-founded by Thomas Say, of “Boatload of Knowledge” and recent BOTW fame) states that “Periodically the question is discussed, what is Dorcus brevis and is it distinct from parallelus? It need hardly be said that this question arises principally among those young in experience and with small series (the ultimate scientific put-down – “You’re a tyro and your sample size was too small.”).”
The Antelope beetle is mainly found east of the Great Plains, and it’s one of five Lucanids in Wisconsin, all of which like wooded areas. Typical of their family, Antelope beetle larvae (grubs) feed in rotting wood/stumps/logs, especially elm, but also basswood, oak, and maple. Adult Lucanids variously feed on vegetation or aphid honeydew. The annual report of the Cornell Agricultural Experiment station in 1891 states that “The adult beetles are found on the trunks of trees and are said, by Harris, to live upon the sap, for procuring which the brushes of their jaws and lips seem designed,” (the BugLady read other sources that say that adults feed on rotting wood). “They lay their eggs in crevices of the bark of trees, especially near the roots. The larvae that hatch from these eggs resemble the well-known white grub (the larva of the May beetle) in form. But unlike the May beetle larva which feeds on the roots of herbaceous plants, the larvae of the stag-beetles bore into the solid wood of the roots and trunks of trees, and reduce it to a substance resembling very coarse sawdust.” Feeding on growing roots is also contrary to other sources that the BugLady read.
Adults will fly to lights at night. Males are collected more commonly than females.
In an aside in bugguide.net we learn that “In Europe, stag beetles are colonizing playgrounds and hiking trails covered with hardwood woodchips.”
SLENDER LIZARD BEETLES (Acropteroxys gracilis) are small (maybe ½”) where Antelope beetles are large, slim where Dorcus is chunky (gracilis means “slender”), and most sport a natty splash of color on the thorax (though some individuals are completely black http://bugguide.net/node/view/501321/bgimage). Like the antelope beetle, they are one of only two members in their genus in North America. Lizard beetles used to have their very own family (Languridae), but for now, they’ve been folded into the Pleasing Fungus beetle family, Erotylidae.
They’re found in a variety of sunny habitats in the eastern two-thirds of the country, north into Canada and south through Guatemala. Adults feed on pollen and vegetation, and their larvae feed within the stems of herbaceous plants, and there-in lies a tale. Adults are found on a variety of flowers and are partial to members of the aster/composite family (plus roses and stinging nettle), but slender lizard beetles are ragweed lovers and are part of an arsenal of North American insects that have been imported to Russia as biological controls of ragweed.
Egg-laying is a multi-step maneuver, as described by researcher Gary Piper in his 1978 paper “Life History of Acropteroxys Gracilis (Coleoptera: Languriidae) on Common Ragweed in Northeastern Ohio”. “Upon locating a suitable stem, a female positioned her body parallel to the stem with the head directed upward and began to prepare the oviposition hole on the basal third of the stem. She first gnawed a fusiform slit through the epidermal and cortical tissues and then proceeded to excavate a smaller hole near the mid-point of the slit. She introduced her head and thorax into the hole and hollowed out an elliptical cavity in the pith. After preparing the cavity, the female advanced up the stem until the tip of her abdomen was positioned above the excavation. She probed for the aperature and, upon its location, inserted the abdomen and attached an egg to the opposite stem wall. There usually was only 1 egg deposited per cavity, but on several occasions 2 eggs were found. Immediately after ovipositing, the female used her mandibles to tease out the stem tissue bordering the hole leading into the pith, thus concealing the egg within. Recent oviposition punctures were white but turned dark brown after several days. The stem also became distended at the point of oviposition ………. Upon hatching, the first instar fed upon the decaying tissue within the oviposition cavity for several days before boring into the pith.”
They eat so much pith that the ragweed stem is weakened and seed production can be affected. The larva overwinters in the stem in a state of suspended animation and pupates there in late spring.
One comment on the beetle’s behavior sent the BugLady down the etymology trail. She read in Piper’s paper that “Adults are thanatotropic and drop from the plant immediately when approached or physically disturbed.” Google kindly kept re-spelling the word and providing un-meaningful meanings (“Showing results for thanatophoric. Did you mean thanatotropic?”) (Um – yes).
The BugLady remembered the poem “Thanatopsis” from high school English, which spurred her to find the Greek root word “Thanatos,” which means “bearing death” and which is akin to a Sanskrit word meaning “it vanished.” A “tropism” (from the Greek “tropos” meaning “a turning”) is, as BugFans certainly recall from high school biology, a response in which an organism turns toward or away from a stimulus. All of which translates into a common beetle habit of feigning death (thanatosis) and dropping off of a leaf when alarmed.
Let’s take this detour a little farther. Thanatosis (some authors do prefer “thanatopsis”) is more than just falling off of a leaf at the first sight of a jumping spider. It usually involves “tonic immobility” or muscular stiffness/paralysis (the insect often tucks in its antennae and legs as it falls), and temporary unresponsiveness to stimuli. The condition persists for varying lengths of time, and the recovery is as fast as the onset.
There are definite survival benefits to the behavioral trait (the longer the swoon the more likely a predator is to leave the swooner alone), and both the tendency to react in this way and the duration of immobility are genetically controlled. BugLady learned of one beetle that enjoys the protection and ministrations of certain ants (and feeds on their offspring); the problem is gaining access to the well-guarded ant hill. The beetle feigns death, is viewed as a carcass by the ants, and is carried home – the perfect plan, except that the beetle risks dismemberment by ants during the journey.
Kate Redmond, The BugLady
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