A relatively cool, moist spring and early summer spelled trouble for this year’s crop of soldier beetles. A few weeks ago a Bug of the Week enthusiast sent remarkable images of dead soldier beetles attached to leaves of hydrangea in her garden. Soldier beetles, a.k.a. leatherwings, are cousins of fireflies and belong to a group of beetles in the superfamily Elateroidea that also includes click beetles and several other beetle families. Like other members of this clan, soldier beetles are natural born killers in both adult and juvenile stages and are highly beneficial rascals to have around the garden.
The juvenile stages are dark grey larvae cloaked in a thick, velvety coat of fine hairs. They are important predators of ground dwelling insects and they will ascend plants to find prey in flowers and on fruit and foliage. I often see large numbers of these hairy rouges in autumn hunting in flowerbeds or on sidewalks and patios. Soldier beetle larvae visit homes in fall when they squeeze beneath the door sweep. When I find them inside, I simply pick them up and return them to the wild. For soldier beetles in Maryland, larvae pass the winter in soil, under leaf litter, or beneath loose bark.
After pupating, adults emerge in spring and in good years they can be found in great numbers on blossoms of perennial plants in flowerbeds. When not consuming nectar and pollen, adults dine on plant pests such as aphids and caterpillars. Mating antics of soldier beetles seem to occur almost nonstop and are quite entertaining. Their rambunctious behaviors have been the subject of several studies. In the soldier beetle dating game, size does matter. For the goldenrod soldier beetle, Chauliognathus pennsylvanicus, biologists discovered that mating females and males were significantly larger than their smaller and less fortunate, non-mating counterparts. It turns out that female soldier beetles are choosy lasses and exercise their prerogative to accept or reject a potential mate. The advantage to large size in males is not so much a “big guy, good look” feature that attracts the females. Apparently, large size enables an amorous male to subdue a coy female beetle more effectively than his smaller competitors whose attentions can be dismissed by the discriminating lady.
A female soldier beetle multitasks with her mate while searching for food on a flower head.
But, it is not all fun and games for soldier beetles in the garden during cool moist seasons. A fungal pathogen called Entomophthora lampyridarum lurks in landscape waiting to infect soldier beetles when conditions are right. After penetrating the surface of the hapless beetle, the fungus takes control of its host and zombie-fies it.
The fungus causes beetles to march to the upper leaves of the plant, clamp onto leaves with their jaws, and spread their wings in the final act of death. This allows fruiting bodies to erupt from the upper surface of the beetle and spew their spores into the environment where they disperse and infect other victims. While we lament the loss of beneficial soldier beetles to their disease, in the greater scheme of things Entomophthora fungi are highly beneficial causing epizootics that can decimate nasty pests like gypsy moths, house flies, and locusts. Some entomologists believe that fungi are the primary regulatory agents of insect outbreaks worldwide. Glad they infect bugs and not us.
Bug of the Week thanks Carol for providing images and inspiration for this week’s episode. The interesting articles “Density Dependent Sexual Selection and Positive Phenotypic Assortative Mating in Natural Populations of the Soldier Beetle, Chauliognathus pennsylvanicus” by Denson Kelly McLain, and “Entomophthora lampyridarum, a fungal pathogen of the soldier beetle, Chauliognathus pennsylvanicus” by G. R. Carner were used as a references for this episode. Enlightening discussions with the king of the insect fungi, Dr. Raymond St. Leger, helped demystify zombie-making fungi.