A friendly picnic beetle, Glischrochilus quadrisignatus, in Seattle.
Sitting outside on a warm summer afternoon, I noticed a dark insect flying slowly nearby. I extended a hand to it and was able to induce it to land. The insect is shown in this picture as it walks to my finger tip. This handsome, shiny beetle is known variously as a picnic beetle, four-spotted sap beetle, or a beer bug. As its names suggest, it is attracted to food and especially to ripe fruits or yeasty smells. Beer and bread dough are both known to attract picnic beetles. And, they are often found on overripe or damaged fruit. They are also attracted to sap exuding from trees. This last behavior has implicated picnic beetles in a more nefarious activity: the transfer of a fungus disease called oak wilt. The beetles are attracted to fermenting odors produced by fungal mats that develop on a wilt-infected oak tree. In feeding on the fungus mat, fungal spores adhere to the beetle's body. The beetles later transfer the spores when they are attracted to feed on sap from a wound on a healthy tree, thereby infecting a new tree with the fungus. The participation in the spread of oak wilt disease is what first drew my attention to picnic beetles. I started my entomological career working on forests insects. But, I have since frequently enjoyed their presence when consuming a beer or food outside.
Picnic beetle on the D key
Tapping I-G
In another encounter with a picnic beetle this summer, I found that it was trying to tell me something. The pictures above depict it crawling on the letters, d-i-g. Dig what? Dig where? Buried treasure? Or was this only the start of the message? Something about my digestive system? Digress? Digitalis? There is no way of knowing as the beetle left after reaching the g key.
Are picnic beetles an Anthropocene species? Do they benefit from human activities? I suspect the answer is yes. You can imagine that the fruits that picnic beetles enjoy might not have existed in such concentrated profusion as they now do in commercial agriculture. There wasn't anything in nature like our vast fields of strawberries or sweet corn prior to the advent of farming. Acres of ripe fruit and vegetables, and food waste in urban areas must have encouraged the growth of picnic beetle numbers, though I haven't seen scientific studies that confirm this idea. Certainly the range of picnic beetles has expanded beyond their native North America. They are now found as far away as Europe and New Zealand. Their travel to these locations across the Atlantic and Pacific Oceans was most likely accomplished through human assistance. So my guess is that human beings have both increased the occurrence of picnic beetles, and have expanded their range in the Anthropocene, making them very much an Anthropocene species - one of the winners in the new epoch. In many respects, these beetles are similar to fruit flies in their relation to human beings. I'll turn to fruit flies in my next post.