Ants of Ithaca

I recently completed Cornell’s excellent Naturalist Outreach class, taught by Dr. Linda Rayor. As a culmination of all my work for that class, I chose to create a field guide to local ants of Ithaca and the immediate surrounding regions for my final project. Fortunately, I had already kept a running list of those I’d found in the short 2+ years I’ve been here, but the experience prompted me to reflect on my past few years of anting. I’ve found 40+ species of ants in Ithaca, which can be seen in my field guide available here.

A preview of my field guide.

Ithaca is located at over 42 degrees latitude north. While similar latitudes on the eastern coast of Massachusetts and New Hampshire enjoy charismatic warmer climate ant fauna such as Bigheaded Ants (Pheidole pilifera), and downstate NY/Hudson Valley sees such interesting fauna as Pheidole, Monomorium, a scattering of southern dolichoderines, and the ever so rare Polyergus and Proceratium, Ithaca shelters no such residents.

Monomorium minimum (the “little black ant”), a common species in the eastern US that is not found in Ithaca.

The bizarre and extremely rare Proceratium, a predator of spider eggs. This is the neotropical Proceratium cf. mexicanum, but more northern Proceratium species are found all around us in Ontario, Massachusetts, and downstate NY, yet not recorded from Ithaca.

Icy and snowy in winter, Ithaca makes life difficult on its resident ants. Cayuga Lake is our closest large body of water, formed by glaciers during the last Ice Age. The lake offers the slightest bit of warmth during the winter, but nowhere near as much as Lake Ontario to the north and the Atlantic Ocean to the east produce on their respective coasts.

A typical winter scene in Ithaca.

As a result, few arboreal species survive here, and the soil living species almost all descend underground when the topsoil freezes in the winter.

Camponotus nearcticus, one of the only arboreal ants in Ithaca that often overwinters far aboveground. These half-frozen ants were found nesting between the cracks of a mostly sound hemlock log.

Our cold, cold past is apparent in the fauna it supports: one of the most common ants in Ithaca is Formica glacialis, which only inhabits areas that were heavily glaciated during the last Ice Age.

A Formica glacialis worker tends some aphids (Aphis nerii) on milkweed.

This common black ant can often be seen running on sidewalks and on plants during warmer parts of the year, a reminder of Ithaca’s natural history. A little further south on the eastern seaboard, Formica glacialis is replaced by the very similar Formica subsericea, which appears to outcompete it in warmer climates.

During warmer months of the year, anting here is easy. As long as there is no severe drought (like this past summer of 2020), ants are easily found in the moist layer of topsoil by flipping rocks and logs, peeling bark, and often simply by watching the ground with a careful eye. Unique environments for ants in our area include preserved wetlands and bogs, as well as glades on the tops of some hills.

Dolichoderus plagiatus, a colorful bog and wetlands specialist ant found in undisturbed habitat.

Stigmatomma pallipes, the “vampire ant”. This predator of geophilomorph centipedes is reasonably common in Ithaca but very cryptic. Workers are found under rocks and will play dead or immediately dig back into the soil, making them difficult to see.

Reproductive alates of all our ants fly throughout these warmer months. Prenolepis imparis flies the earliest out of all our species in early spring, soon after ground thaw in March, with Lasius claviger alates bringing up the rear around November, often weeks after our first snowfall.

The cooler months of spring and fall see much of the same ant fauna, but Stenamma, a genus of soil loving and secretive small brown ants, are more commonly found in these chillier months. Nobody is really sure why, and very little is known of their biology.

Two dealate Stenamma queens found in Ithaca, about to start their own nest.

The winter months of Ithaca are the saddest times for most entomologists. Besides a few of our strange winter specialist insects, most arthropods hunker down for the winter.

Not an ant: a wingless winter specialist cnypid gall wasp found walking on the snow in December.

The two ants that can be reliably found outdoors in these times are Prenolepis imparis workers and Lasius claviger dealate queens.

Prenolepis imparis are also called “winter ants” and are adapted to withstand freezing temperatures while foraging for food in the winter.

Lasius claviger queens are socially parasitic for their founding stage on other Lasius species. They use the colder temperatures to their advantage to sneak into host nests while all the other ants are hardly moving. These dealate queens can often be seen walking on snow, looking for a host nest.

Perhaps it is because of this frigid climate, or maybe just dumb luck, that the area has avoided the absolute worst of invasive species for now. 3 introduced species are present in the area.

Immigrant Pavement Ants (Tetramorium immigrans) are abundant in open sunny areas such as sidewalks. In the spring and fall where their territory lines are redrawn, colonies host huge wrestling matches on sidewalks. Because the ants are all about the same size and evenly matched, these fights quickly descend into stalemates, with hundreds of ants locked together for hours in a competitive embrace.

Tetramorium immigrans worker found under a rock.

An Asian species of crazy ant (Nylanderia flavipes) has made it to Ithaca mostly unnoticed until I found it nearly everywhere in Ithaca in 2018. Local ant enthusiast Norm Trigonoff had found this tiny species before I came here and holds some of the earliest records in our area.

A worker Nylanderia flavipes greets her fellow male nestmate. Male ants look hardly anything like their sisters and are relatively short-lived in comparison.

Finally, the European Fire Ant (Myrmica rubra) is known in our area from a few spots in suburban Ithaca. Hopefully it stays low abundance in our area as it has until now, but there is no way of telling for certain but to wait and see. Much more aggressive than our native Myrmica, this species stings readily and painfully!

An angry European Fire Ant (Myrmica rubra) searches for a photographer to sting.

Of course, this field guide is not an exhaustive faunal list: Antmaps lists 127 species from NY at the time of this writing. Not all of these are in our area, but there are sure to be local species I have missed in my collecting. However, I hope it serves as a good foundation for any local ant fans to get started and learn a few of our more common ants!