Myrmecology: (mərməˈkäləjē) the branch of entomology that deals with ants. From the Greek myrmēx, or myrmēk, meaning ‘ant’
This week the Wild Davis course got to learn a fun new scientific word AND perform bait-trap surveys of ant populations in the southwest end of the Arboretum (near the White Flower Garden Gazebo). Our study questions related to bait preference and diversity of ant species in the area, particularly the diversity of native and introduced/invasive ant species. Sharon set out traps prior to class using peanut butter, pecan sandies, and canned tuna as bait. To help us with identification, we enlisted the aid of the wonderful and abundantly-knowledgeable Phil Ward in the Entomology Department here at UC Davis*.
Our study consisted of two parts: first, observe the abundances and diversity of ants on the different baits, noting environmental factors of the bait locations to determine what sorts of habitats recruit more ants to the bait; second, collect ants of each species we find for contribution to the Citizen Science project School of Ants, started by Phil’s former student Dr. Andrea Lucky. School of Ants uses student- and community- collected ants to track distributions of ant species across the entire United States. All you have to do is collect ants and mail them to Dr. Lucky at the University of Florida for identification!
The first part of our study ran into a little problem. It turns out that ants are not the only organisms in the Arboretum that are attracted to peanut butter, cookies, and tuna. Many of our bait traps (particularly those in the sun, which were more exposed and visible) were raided by scrub jays, mallards, ground squirrels, and even other insects. The ants preferred the shady baits, so we got a good selection anyhow.
Our baits (which were within the landscaped beds and lawns around the gazebo) produced three species of ant:
- the Argentine ant (Linepithema humile): a small, thin, grayish-brown ant native to (take a guess!) Argentina and other parts of south America. They were first found in California in the early 1900s (likely introduced through nursery plants) and are known for their aggression towards native species, frequently driving them to extinction. They prefer irrigated areas (like watered lawns and flower beds!) and so are common throughout the managed parts of the Arboretum.
- the Pavement ant (Tetramorium immigrans): native to central Europe and also introduced in California, this ant is one of the most commonly found introduced ants in North America and gets its common name from his preference for urban habitat (including roadsides, pavement cracks, and buildings).
- the Winter Honey ant (Prenolepis imparis): a common native California ant; one of the few native species that can persist in areas taken over by Argentine ants, likely due to differences in diurnal activity. These ants build deep underground nests and forage during times of year that are cooler than when most other ants are active (hence their common name of ‘winter’), meaning they compete less directly with other species, like the Argentine ant.
As you can see in the photos, we found ants on all types of baits. They appeared to slightly prefer the cookies first, the peanut butter second, and the tuna third, though if we found ants at one bait in the location, we often found them at all three (assuming all three baits were unraided by other organisms).
Dr. Ward had brought along a pooter (that’s a real scientific tool for collecting ants. I did not make up the name) to help us easily collect ants off the bait. A pooter is a length of flexible rubber tubing with a filter about an inch from one end. You put that end near the ant to be collected, put your mouth on the other and and inhale. The ant is sucked up, caught by the filter (so you don’t inhale it) and you can trap it there with your thumb long enough to drop it into a baggie. Dr. Ward collected (pooted?) samples of each species of ant we found on the baits using this method. This was easily the most entertaining portion of the class.
Near the gazebo is a less managed area of Arboretum land that houses a variety of native species. Since this area is not irrigated, it is too dry for the Argentine ants and provides a refuge for native species. Dr. Ward walked us through this area, showing us how to identify nests and individuals of different native species. We found evidence (nests or actual ants) of three additional native species:
- Pheidole californica: this native ant is one of several species of seed-collecting ants. There were many of their nests visible along the path we walked, though in the heat of the afternoon, no actual ants were visible. If you look closely at the photo of the nest below, you will see that the orange pieces of the nest are actually small seeds harvested by the ants from nearby plants.
- the field ant (Formica moki): the nest of this species was spotted by yours truly (but who’s counting? :-D), with many workers running around. And I do mean running! A clear photo was rather difficult
- the velvety tree ant (Liometopum occidnetale): this native ant was my particular favorite, nesting in an oak tree and scurrying over the entire trunk. The ants also have a particular smell – something akin to spoiled milk or vinegar. This ant also has an interesting ecology, with several other insect species in symbiosis either as parasites, mimics, or co-inhabitors of the nest. If the velvety tree ant is lost (for example, due to invasion by Argentine ants), their symbionts are also at risk.
Dr. Ward again used the pooter to collect ants of each of the native species we found. Formica moki ants produce formic acid, which Dr. Ward got a coughing lungfull of when he collected them – a generous sacrifice in the name of citizen science!
This class period may have been my favorite thus far in the Wild Davis class. It was a great chance to show the students the diversity and ecological importance of a group of organisms that are often overlooked, and a great chance to showcase the depth and breadth of knowledge that students have access to in their professors here on campus. Sharon and I are grateful to Dr. Ward for his contribution to this making this session such a success, and we look forward to contributing the specimens he collected to the School of Ants database!
*all ant information presented here is reproduced from Dr. Ward’s conversations with the Wild Davis students, from the Ant Guide Dr. Ward developed for the Arboretum, or from Dr. Ward’s research page and links therein.