BEWARE THE BLISTER BEETLE

The Male Blister Beetle's Poison Deters Predators but Attracts Females Like Perfume

The big beetle flying unsteadily toward the hilltop on which I stand seems not to know exactly where it is going. It turns away but then circles back, heading into the wind before plopping heavily onto a brittlebush a dozen yards downslope. When I reach the shrub, I see that the beetle has found a flowering bush festooned with other members of its species, Lytta magister. The magisterial black and orange beetles dangle like garish earrings from the yellow blooms. This is spring in the desert, the season when the Lytta magister congregate for a brief but intense time of mating. The brittlebush is filled with pairs tied together so tightly, abdomen tip to abdomen tip, that one beetle can support the entire weight of a partner suspended in space. The few remaining unpaired males tenaciously court the uncoupled females. An unusually small male perches on an extralarge female, lashing her antennae in what proves to be a futile attempt to persuade her to become his. The failure of the small male to convince a larger female to mate is characteristic of the Lytta magister, a species in which large beetles invariably mate with other large ones, while medium-size males pair with medium-size females, and small ones seek other small beetles. But once a couple gets together, they are slow to part, often mating for as long as 24 to 48 hours. Both the size-matched pairings and long matings may be linked to yet another unusual feature of this beetle, namely its poisonous blood. Pick up a Lytta magister, and you will soon find a sticky, acrid-smelling yellow fluid oozing about its legs and then onto your fingers. The fluid is the insect's blood, which it can release at will from joints in its legs. The blood contains a particularly nasty substance called cantharidin, which induces blistering, among other things. This is why the Lytta magister belongs to that group called blister beetles. The poisonous, bad-tasting secretions are designed to deter insect-eating mammals and birds. The bright colors of the blister beetles provide a vivid warning to hungry predators not to touch. The cantharidin, an important chemical weapon for blister beetles, brings us back to their sex lives. The females apparently do not have the biochemical pathways needed to synthesize cantharidin on their own. But the males do, and they are "generous" enough to share the production with their mates. The sharing occurs during copulation, when males pass cantharidin along with sperm to their mates, a slow process that contributes to the extraordinary length of blister beetle mating. Once the female has received the cantharidin, she becomes more poisonous herself and can coat her eggs with the chemical, making them unappealing to hungry ants that might otherwise extract them from the ground in which they are laid. Because males donate valuable cantharidin to their mates, females benefit by mating with the largest males around, those with the potential to provide extra quantities of the toxin. And because males have something useful to pass on to their mates, they too benefit from being choosy: Those males able to mate with large, fecund females will father more young than males whose smaller sexual companions have fewer eggs in their ovaries to fertilize. The lengthy and elaborate courtship of these beetles apparently permits both sexes to evaluate each other's size. As a result of the universal preference for large partners, large females allow only large males to mate with them, leaving the smaller beetles to do the best they can with the wallflowers. Once paired, the beetles feast together on the flowers of brittlebush and other desert plants, crawling short distances from one flower-rich shrub to another over a few days, with one partner more or less dragging the other along. Then the pairs begin to separate, and the beetles depart, each one struggling to become airborne. The females are off to search for clusters of grasshopper eggs buried in the ground where they will lay their cantharidincoated eggs. Upon hatching, the blister beetle larvae will feed on the grasshopper eggs. The next spring, a new generation of adults will emerge from the ground and set off to find others of their kind. But for now, the shrubs that once swarmed with the big black and orange beetles are empty again. The party is over for another year.