Lasius (Dendrolasius) fuliginosus, is an European ant species of the subfamily Formicinae. The species’ name means “sooty” or “dark”, referring seemly to the very dark, shiny color of the ant. The ants are really black (unless other dark Lasius species, which are actually brown) and shiny, making them very appealing to look at. They are also slightly larger than other Lasius species. The ants have a distinctive odor (pick one up and smell your fingers!) and nest in hollow trees, and therefore are also called the smelling carpenter ants. The nest is built using cardboard-like material made of wood particles, honeydew and a species of fungus (Cladosporium myrmecophilum). The workers can sometimes be seen moving up and down a tree in a trail, with the abdomens of the returning workers being physogastric of the collected honeydew. Their trails can be very long, sometimes up to 30 meters, providing an amazing spectacle to observe.
However, the more interesting part of their biology is the way they found their colonies. Lasius fuliginosus is a social parasite… of a social parasite. The female enters a colony of the yellow-colored Lasius umbratus, manages to take over its odor, kills its queen and takes it over. Lasius umbratus in its turn does the same to Lasius niger. The Lasius fuliginosus female cannot found a colony independently and relies entirely on the Lasius umbratus workers to raise her brood. When the yellow Lasius umbratus workers decrease and the Lasius fuliginosus workers increase in numbers, the colony slowly makes a shift from a predominantly yellow color to a predominantly black color, until the last Lasius umbratus worker dies, erasing every single trace of the conquered colony.
The dependent colony foundation is one of the main reasons what makes it so hard to keep this species. There are very few cases of successful foundations. On the one side, I find this a shame, because it prevents the ant-keeper from observing their interesting behavior and enjoying their beauty, but on the other side the challenge keeps stimulating the ant-keeper’s interest.
You’ll need a Lasius umbratus colony and a fertilized Lasius fuliginosus female to raise a colony. However, it is also possible to raise a colony without Lasius umbratus, but by using Lasius niger as a host colony instead. The latter is what I’ve done. I found a Lasius fuliginosus female in May 2012, which I then introduced to 20-30 Lasius niger workers in a test tube. She was accepted by the workers and a month later, in June, I boosted the “colony” with some brood, only to find that the female had laid some eggs. You have to be very patient, because the fertility of this species is delayed. It can take some time before the first eggs appear. In August the first larvae appeared (see picture below). Although I was very excited, I was also skeptical, because this did not yet prove that the female was fertilized. The eggs could still have been unfertilized, only to produce males.
The larvae did not develop into pupae before the winter arrived and I decided to put the colony in the refrigerator in order to induce dormancy. Perhaps the rest could help the colony to develop. I ended the dormancy in February 2013. In April, the colony had produced two pupae. The queen kept producing eggs and the numbers of larvae and pupae increased substantially.
On May 22nd, I took another look at the test tube and when observing all pupae I came across one through which I could see the adult moving inside. There were also other open cocoons, but I could not see any Lasius fuliginosus workers between all the Lasius niger workers. So I decided to help this one out. Her mandibles were already sticking out. I took her out the test tube and gently cut open the cocoon, releasing the adult Lasius fuliginosus worker. After putting her back in the foraging area of the colony, many Lasius niger workers started inspecting her and then dragging her. She wasn’t able to walk. Perhaps the conditions in which I’ve helped her hatch were not humid enough, which caused a problem in the hardening of her exoskeleton. Eventually she was dragged into the test tube by the Lasius niger workers. I wasn’t sure if she was under attack and would end up as food. When I took a look inside the test tube, she unfortunately seemed dead. After looking again a few hours later, I could not spot her. The Lasius niger workers probably took care of her dead body. You can see her (while still alive) in the picture below.
I did not give up. The queen was doing fine, producing a lot of brood. There were still many eggs, larvae and pupae, but no adult Lasius fuliginosus workers. I proved that the larvae can survive without the fungus and that the eggs are viable, but something went wrong during or after the hatching of the cocoon. I was disappointed, but I still had hope.
I looked in the test tube again on June 5th 2013, and suddenly there were several Lasius fuliginosus workers between all the Lasius niger workers. They were totally healthy, accepted and functioning. There was apparently no need for me to help them hatch, because the Lasius niger workers can do the job on their own. I decided to disturb the colony as little as possible, which was kind of hard, because I wanted to watch all the time. The founding was hereby successful more than a year later from the moment I found the queen. The colony is still doing fine today, the Lasius fuliginosus workers increasing in numbers (see picture below). Now let’s hope the colony maintains as long as possible. Remarks on the care of the colony are welcome.
I hope this post can provide some information to other ant keepers about the biology and the founding of Lasius fuliginosus. My main advice to others would be to be patient. It took me more than a year to see the first adult worker, only to see her die tragically immediately after hatching! I also hope that other hobbyists can contribute to my knowledge and help me take care of this Lasius fuliginosus colony. I would also love to hear from other ant keepers that have successfully founded a Lasius fuliginosus colony. If you have some tips, suggestions or other remarks, please don’t hesitate to leave a comment.
More information about the colony founding in this species can be found here (Donisthorpe, 1922).