Let’s start the New Year with some unfinished business from the old. A few weeks ago, a short video appeared in the Bug of the Week email inbox from a concerned friend assailed by a horde of suspicious looking insects swarming near the front of his home. Dark amber in color, hyaline wings, vast numbers of insects scrambled near the house and took flight. Sights like this strike fear in the hearts of wooden-framed home owners across much of our country. Could this be an infestation of the “invisible destroyers”, eastern subterranean termites? In the natural world, eastern subterranean termites live in underground nests and arise from the earth to forage on fallen trees. Remarkable creatures are these, with the ability to perform a digestive magic trick unparalleled in the human world. They consume wood. To utilize nutrients tied up in a biopolymer hard enough to dull an axe blade, most termites rely on symbiotic bacteria in their gut to digest the rugged plant material called cellulose. Some primitive species of termites enlist unicellular organisms called protozoa to accomplish this feat. Termites have an unusual and rather crude way of passing these vital microbes from one termite to the next. They employ a process known as proctodeal trophallaxis. One termite excretes a droplet of microbe-packed fluid from its anus. This packet of goodies is consumed by another termite waiting at the rear end. Yum! In addition to the transfer of vital symbionts from one termite to the next, trophallaxis is also a way of disseminating chemical messages called pheromones that regulate the development and behavior of termites within the colony. With the advent of domestic structures, termites have discovered a bountiful source of food provided by humankind. Termites colonize and establish residence within a home if conditions of moisture and temperatures suffice. They reach the structural wood of buildings by constructing tunnels of soil, wood, saliva, and excrement from an outdoor colony, which are built up the side of foundation walls until they reach the wood of a sill plate or floor joist. Then they enter the home. The appearance of swarming winged termites near a home may be the harbinger of problems down the road and the presence of swarming termites inside your home is a sure-fire indication of an infestation. Eastern subterranean termites are estimated to cause several billion dollars of loss annually associated with repairs, treatments, and prevention of infestations. Little wonder my friend was concerned.
Whoa, is this holiday visit a swarm of termites? Nope, citronella ants like these make an annual appearance at my home during December here in the DMV. Watch winged adults with narrow waists, forewings and hindwings that differ in size and shape, and elbowed antennae mill around before taking flight. A few wingless orange workers also stroll by. Termites like these infesting steps in my backyard usually swarm in spring. With thorax and abdomen broadly joined, forewings and hindwings similar in size and shape, and antennae resembling a string of beads, they are easy to distinguish from ants.
Ah, but the holiday season is not the usual time of year eastern subterranean termites swarm throughout most of our land. Here in the DMV my home-grown termites make their flighted appearance in spring, as we saw in a previous episode. But what to my wondering eyes did appear two days before Christmas in this very year? Swarms of citronella ants. The appearance of winged citronella ants emerging from beneath my front sidewalk was a welcome surprise in this somewhat dismal season for observing insects and their kin in the DMV. Ants often emerge from the earth and swarm to mate and found new colonies in warmer months in temperate regions. However, ants in the genus Lasius have been observed emerging from the earth in Maryland in late autumn and, at my home, in early winter. Lasius ants go by many colorful names including citronella ant, yellow ant, and lemon ant. The lemony scent we know as citronella owes to a compound found in many plants, including lemon, lemon grass, and several species of eucalyptus. Special glands near the jaws of Lasius ants produce aromatic lemon-scented citronellal. When threatened by an intruder, citronella ants send out an alarm by releasing citronellal. This pheromone brings nest mates running to assist in the defense of the colony. In addition to the well-known insect repellency of citronella, citronella ants have one more chemical trick up their sleeve, or should we say, in their rear end. Glands near the tip of the abdomen produce irritating formic acid. Formic acid contacting the eyes or face of an attacking predator serves as a powerful deterrent. This type of chemical warfare is an important strategy used by many species of ants. Fortunately, Lasius ants are not wood destroyers like their cousins the carpenter ants. In addition to hunting soft-bodied prey, Lasius are herders. Yes, that’s right, they actually shepherd root-feeding aphids, moving them from the roots of one plant to another to optimize the production of nutrient rich honeydew excreted by the aphids, upon which the ants feed.
Now returning to the plight of my insect-plagued friend, a quick look at his video soon gave me to know he had nothing to dread. Termites can be readily differentiated from ants by examining these features: shape of the antennae, width of the waist (in bug-speak, where the thorax joins the abdomen), and, for winged adults, the size and shape of the wings. Termites have simple antennae that look like a string of many beads. Ants have jointed antennae with a prominent elbow near the middle. Termites have a broad waist where thorax meets abdomen. Ants have a narrow, a.k.a. wasp-waist, where thorax meets abdomen. Termites have forewings and hindwings similar in size, shape, and texture with many fine small veins. Ants have large forewings, smaller hindwings, both with few prominent veins.
If you see swarms of insects emerging from the earth during this mild winter, fear not as these are likely citronella ants. Later in the year be on the lookout for termite swarms outside or inside the home. Using the information in this episode, we hope you will be able to tell these rascals from each other.
Inspiration for this episode came from my friend Mike who shared his video of citronella ants. We also mourn the passing of our friend and colleague E. O. Wilson, whose love of insects and the natural world inspired entomologists, biologists, conservationists, and naturalists around the world for more than six decades. As a youngster, Ed Wilson studied citronella ants in Rock Creek Park here in the DMV. The study of ants became his life-long passion and ants served as a model for our understanding of insect and human societies. We also thank my friend and colleague Dr. Barbara Thorne who studied termites under her life-long mentor and friend E. O. Wilson. Dr. Nancy Breisch, one of Dr. Thorne’s students, assisted in creating this episode.