ECOVIEWS: Yellowjackets' disappearance has logical explanation

The Tuscaloosa News
Eastern yellowjackets, which are attracted to hummingbird feeders, may be victims of invasive red imported fire ants.

Q.  I live in Tennessee. Each year I see numerous yellowjackets around my compost pile and hummingbird feeders. This year I have seen virtually none. Has there been a notable decline in hornets and other wasps in this region that would explain their disappearance?

A. The perceived absence of any animal in a given area can have various explanations. One is that the species has not actually declined in numbers; it simply has not been observed as often as in the previous year purely by chance. Another explanation: Many animal populations fluctuate naturally through cycles of abundance and scarcity. A species may be abundant one year and absent the next. I received two queries in one week from the same town in Alabama. One asked why the blue jays had disappeared that year. The other asked why blue jays had become so abundant. Perhaps the second person had more attractive bird feeders.

Two ubiquitous culprits of declines in some species, especially insects, are (1) indiscriminate use of pesticides and (2) establishment of a nonnative invasive species in a region. The invader could be the carrier of a disease to which a native species has no immunity. Or the invasive species could be a predator with no natural enemies, such as the so-called murder hornet now found in the Pacific Northwest.

For an answer to why yellowjackets in a particular region might have declined, I turned to University of Georgia entomologist Robert Matthews, an expert in the ecology of yellowjackets and other social wasps. As it turns out, Bob had witnessed a similar decline in yellowjackets during the 1980s.

“The question immediately took me back to a time when I and others noticed a similar phenomenon in the Athens, Georgia, area where I had been actively studying yellowjackets for about 10 years. In 1983 they virtually disappeared, after having reliably large populations present every season prior to then. There followed several very low years where I could scarcely find a nest or attract workers to baits. The past few years have seen them return in relatively large but not overwhelming numbers.

“The early 1980s coincided with the time when red imported fire ants (RIFA) first were recorded in the Athens area as they spread eastward and northward following their initial discovery around Mobile, Alabama, in the early 1940s. The present RIFA distribution includes much of southern Tennessee with occasional confirmed nests from Kentucky, indicating that RIFA continue to expand their range northward.” 

Invasive fire ants are a scourge, and many animal species, including humans, have suffered greatly from them. According to Bob: “Yellowjacket colonies are annual, dying out after the first frosts, with only fertilized queens surviving winters in protected sites such as decaying logs. These queens emerge and establish new nests solitarily in late spring, typically underground in small cavities such as old rodent burrows, decayed root traces, or lawns and gardens with disturbed soil. RIFA also prefer to establish colonies in disturbed habitats such as pastures, roadsides, lawns, and gardens.

“RIFA are voracious predators and scavengers. My speculation (and what I now believe may have occurred in Athens in the early1980s) is that foraging fire ant workers are likely to discover undefended (hence vulnerable) queen yellowjacket nests, They then recruit foragers to harvest the booty, easily overwhelming the queen who must leave her nest unattended for extended periods while she hunts for food to give her developing first brood. My hunch is that the area of Tennessee where your query originated is one involved in the present wave of RIFA expansion and that RIFA is the root cause of the population decline noted by the reader.”

To proceed from hunch to proof would require entomological research in the region. In the meantime, Bob’s explanation sounds plausible to me.

Whit Gibbons is professor of zoology and senior biologist at the University of Georgia’s Savannah River Ecology Laboratory. If you have an environmental question or comment, e-mail

Whit Gibbons