Paul Snyder, The Operations Manager of Secrest Arboretum in Wooster, OH, informed Jeni Filbrun, the United Titanium BugZoo Manager, about a strange ant species that he observed making nests on the twigs of Cornus sanguinea, commonly known as 'Anny's Winter Orange' or ‘bloodtwig dogwood’. Jeni brought a few twigs with ant ‘nests’ to the Entomology Department to rear them and possibly make a display colony in the BugZoo.
These ants build ‘nest-like’ constructions around the twigs. Ants were seen around the ‘nest’, and I collected a few ants to run the taxonomic key for species identification.
Taxonomy and identification.
Using the comprehensive ant ID guides in Kayla Perry’s Lab, we identified these ants as Crematogaster cerasi. This species is widely distributed in North America. There are 28 species of Crematogaster ants documented in North America and closer to 500 species in the world.
Crematogaster ants can be identified using several characters: 11 segmented antennae, flattened petiole, and heart-shaped gaster that is flattened dorsally. The ants in the genus Crematogaster, are capable of bending their abdomen over the alitrunk when threatened, accounting for their name ‘acrobat ants’.
C. cerasi is about 3.2 mm in length on average. This species has more appressed hairs on the head and gaster. Long erect hairs can be seen on the humeral (shoulder) angle on the pronotum, and the dorsal surface of the thorax has longitudinal short, fine ridges. Overall, they are dark in color, but the head and alitrunk are dark yellowish brown while the gaster is black and glossy. The propodium has two spines that are often slightly wavy along the top margin.
Habitat
Once we had confirmed the identification, we were interested in the ecology of this ant species. The species description in the key listed the nesting habitat as fallen logs, stumps, or under trees. It did not describe nests in arboreal environments. This was intriguing! We carefully opened the nest material that wrapped around the twig. There were hundreds of aphids around the twig, underneath the cover, and they were being protected by the ants. Also, we observed some ants tending and extracting honeydew from them.
In this mutualistic relationship, ants protect aphids from predators, sometimes even transporting them to better feeding sites. In return, the aphids produce a sugary substance called honeydew, which ants consume as a food source. The ants constructed the protective casings from chewed plant material, and this cover added another layer of security for the aphids, ensuring their survival and continued production of honeydew.
This mutualism is a classic example of how different species can benefit from working together, with each party providing something that the other needs to thrive. However, because these ants tend and protect aphids, some consider Crematogaster cerasi as an agricultural pest.
In addition to aphids, these ants have been reported tending scale insects including calico scales (Eulecanium cerasorum) and magnolia scales (Neolecanium cornuparvum) (Vanek, S., D. Potter. 2010).
Life cycle
Ant workers typically start foraging early in the spring. After male and female alates are produced by the queen, mating occurs in the summer, and nuptial flights can be seen in July and August. Females mate only once in their life, and the males die shortly after mating.
After mating, the queen searches for a place to build the new colony. The queen sheds her wings and searches for cavities in the soil, logs, or any other suitable place to lay her first batch of eggs. The emerging workers (females) are tended by the queen until they take over the task of building the nest and take over the other tasks within the nest. The queen continues to produce offspring throughout her life using stored sperm to expand the colony.