A Look at Two Lasius In My Yard

I was out in the garden today digging around to plant some 215 Liatris corms when I naturally started breaking into ant nests on accident. The two I'd like to focus on are species of Lasius that look very similar.

 

Lasius claviger is the slightly smaller of the two at about 3 or 4mm long. They're a brighter orange yellow color and their eyes are relatively small in comparison to their head.

Lasius umbratus is slightly larger at maybe 4 or 5mm long. They're not as bright looking but rather a richer shade of orange learning more toward brown than yellow. And their eyes are larger in comparison to their head. They're also slightly duller looking, and not as shiny as L. claviger.

Both species live almost entirely underground though I've noticed L. claviger sticks with soil nests wherever there are the roots to trees and large shrubs. While L. umbratus more often nest in mixed nests of rotting wood and soil, and I'd associate them more living along side termites. 

While all this is well and good, I've noticed there are perhaps 4 species in yard. What I'm calling L. umbratus is at least one species here, though maybe not L. umbratus itself, certainly something in the umbratus group. What I'm calling L. claviger however seems to have at least 3 forms. L. interjectus I'm sure is one and differs only in that the hairs along the gaster are more parted than the L. claviger. The third version is almost completely yellow, smaller looking, and more easily stirred into producing the citronella odor. I didn't encounter this one today but if I find them again I'll try and get pictures, key it out, and report back. They seem to be completely devoted to wet muddy clay soil though as I've never seen them when it's dry out.

Ants on the Aster Family

It's fall time and the last of the ant nuptial flights have been underway for a few weeks now. It's only appropriate that this happens with the last of the blooms too. 

Lasius claviger and Lasius umbratus queens emerge from nests during the afternoon hours.

For some reason I find lots of them hanging out in goldenrod plants that are still in bloom, but only during the hours of the nuptial flight itself. Come darkness they disband and take to the ground looking for a host colonies.

I'm not sure what it is about goldenrod that attracts them so. This isn't the result of a colony under the plant and the queens simply trying to climb up high to take off. Many of the queens are stationary on the plant and have shed their wings.

The only thing I can come up with is they're attracted to the light scent the flowers give off. In case you're wondering this plant is Solidago gigantea. It's one of the tallest goldenrods in North America. Online sources say it gets up to 8' but I've seen it surpass 10' on some years.

So this got me thinking, maybe they're not attracted to just Goldenrods but perhaps other plants in the composite family.

Sure enough upon inspecting my New England Aster I found a queen or two on the plant. However, I was only able to find two total.

And these were trying to take off. They were not being relatively stationary on the plant. So it's looking like they're only attracted to Goldenrods that are in bloom. I checked other plants as well and couldn't find them on anything else.

Lasius Ants in North America

Lasius is such a diverse genus of ants. These are small/medium sized ants about 3mm to 6mm. "Ants of North America," lists 33 species in back of the book. Species in this genus have been divided into 4 groups, niger, flavus, umbratus, and claviger. The niger group (pronounced nyjer!) boasts big healthy looking queens that have enough stored food to start colonies on their own. In the ant world this isn't saying much, queens in assorted ant genera do it all the time. But in the Lasius group it's worth pointing out.


Here is a Lasius (niger) neoniger queen with two darkly colored workers. Queens in the flavus group are also capable of starting colonies on their own. Species in the flavus group tend to be smaller and more orange/brown in color. Workers in the flavus group also tend to be orange in color.

In order to talk about the umbratus and claviger groups one has to learn how colonies are founded first. Overpopulation and limited nesting space has driven queen ants to sometimes band together and tolerate one another's presence until the first workers are born. This saves the queen ant the trouble of killing the other 40 or so queen ants who've all decided to start a colony under the same rock. The result is a massive colony that suddenly appears some weeks later.

But there is an issue here. With so many queen ants in the colony, the next generation of reproductives won't have enough food to start colonies of their own. So after the first workers are born an internal power struggle occurs. Workers will slowly kill off queen ants in the colony. As they begin foraging other small colonies might be discovered. These are either killed immediately or integrated into the new colony. Eventually though all but one queen is left the new colony and she becomes the primary egg layer. (Occasionally the last queen standing may die of her injuries too.)

This system has lead to a number of evolutions. Firstly queens that band together tend to be more successful becuase they produce more workers then the starting colonies around them and are better able to deal with stronger colonies that have been around longer. There are two flaws though.


1) Queens aren't picky about what species of Lasius queen they start a nest with. Pictured above are two queens of Lasius neoniger and one queen of Lasius alienus stating a colony. The L. neoniger queens tend to be much better parents and care for the eggs when disturbed.

2) The first workers of the colony don't always choose the strongest queen to be the primary egg layer. Simply saving your energy and appearing to be the best queen is more important than actually being the best choice. It's this that umbratus and claviger species take advantage of.


Both claviger and umbratus queens tend to be slimmer, they don't have as much stored food in their abdomen, and they require an existing colony of Lasius to start a nest. Queens in the claviger and umbratus groups are social parasites of species in the niger group.

Having to successfully sneak into a colony and replace it's queen without the workers getting wise is a tricky business. Over millions of years these social parasites have learned a number of tricks. Playing dead to be brought in the nest as food, sneaking in the nest before the workers have started favoring and killing queens, spraying citronella odors to confuse workers, and out right badging in the colony entrance are just a few methods observed over the years. Even with such a variety of methods to employ success is still very low.


Ants rarely give up though and social parasites also employ the oldest trick in the ant book, overwhelming numbers. Social Parasitic species of Lasius out number their hosts 10 to 1. Their nuptial flights are 10 times bigger. Every year a colony of Lasius claviger completely covers my front steps in flying ants.


Easily a couple thousand queens pour out of each colony and continue to do so for day. Queens land after mating and begin their task of taking over a colony. Once completed, the host workers will take care of the parasitic queen's brood and slowly the colony changes it's colors.




In a matter of 12 or so weeks the entire workforce is now that of parasitic species.



The host species simply dies out. Though the queens need assistance to start a colony, her workers are more then capable of taking it from here.


Underground root aphids prevent the need for foraging on the surface. Umbratus, claviger (and I want to say flavus but I'm not certain,) forage almost exclusively underground. They emerge above ground only during their mating season.


The honeydew from the aphids is nutritious enough to feed the whole colony. The occasional dead worm also makes it's way into the mix though.


Cocoons are incubated near the surface under stones or logs.

The only real difference between umbratus and claviger group species is that claviger is known for producing the citronella odor. Gardeners are probably most familiar with it. Accidentally digging up part of a colony fills the air with a sweet lemony scent.