Lasius niger on peony flower buds

This is a new behaviour for me, so perhaps others can fill me in.

We have two different peonies in our garden planted right next to each other; either different species or varieties. The flower buds on one of them is currently covered in black garden ants Lasius niger, which are clearly attending them for some reason. The other peony has no ants - not one - on the flower buds.

I spent some time yesterday watching and photographing the behaviour and still can't explain it. There are no aphids, so it can't be honeydew, and I can't see any obvious extra-floral nectaries. The ants' attentions seem to be focused on the sides of what are probably  sepals but may be developing petals (see photo).

Lasius niger on garden peony © M. J. Lush, 2013

Most of the time when I see ants on plants they are attending homoptera, so the relationship is unlikely to be very beneficial to the plants. This may be one case that is really advantageous to the plant, but I don't see what the ants are getting out of it or why they are only on one of the two plants.

Is this familiar to anyone?

Lasius neglectus found in the UK

According to a BBC News report released yesterday the invasive species Lasius neglectus has been found in Gloucestershire in the UK.

For those who are unaware of L. neglectus, it is a relatively newly discovered invasive ant species. It has been marching across Europe and, because it does not seem to be too bothered by cold conditions, a number of myrmecologists have been predicting that it will become or was already established in the UK, making it the first non-native ant that could survive away from heated buildings. The question was how long it would take for its presence to be realised, as it looks very similar to the common black garden ant Lasius niger.

More information on the identification, biology and status of L. neglectus.

Separating Lasius niger and Lasius platythorax workers

By popular request! Well, one person requested it anyway.

Lasius niger and Lasius platythorax are undoubtedly hard to separate. This becomes particularly difficult when you find specimens that seem to be somewhere in between. However, it is always possible to assign them to one species or another, with a bit of work.

First of all, L. niger and L. platythorax are small dark brown Lasius with outstanding hairs on their antennal scapes. In the UK there are no other species that have these characteristics, though in Europe it gets a little more complicated¹.

Some people seem to base identification of the workers of these species on one or two characteristics. However, experience has taught me that it is usually more reliable to use all of the following:

• Density of pubescence on the clypeus
• Shape of propodeum in profile
• Setae length on the mesosoma
• Shape of clypeus in profile

These are all shown in the photomontages. I have, on occasion, also felt the need to use the length of the setae on the underside of the head, but I can usually identify these species reliably without this and the setae are difficult to measure.

Probably the most useful character is the clypeal pubescence. Quite often this can be visually assessed, with practice, though on occasions an entire nest series will have moderate clypeal pubescence and have to be assessed morphometrically. To do this you use a measuring line, as shown below. Measure the length of this line in µm (l) and then count the number of hairs that intersect it (n). Seifert (2007) gives the average distance between the hairs (l/n) for L. niger as <16µm and for L. platythorax as >19µm.

Clypeal pubescence in Lasius niger. Measuring line shown in red.

Clypeal pubescence in Lasius platythorax. Measuring line shown in red.

Whilst you're looking at the clypeus it's worth noting its shape in profile. Typically, L. niger has a rather curved clypeus, whilst in L. platythorax it is comparatively straight. The idea that they differ has been floating around in BWARS for a couple years now, though I must admit I'm one of the last to accept that this is probably a good character. I feel like I've now seen enough and have not been able to dispute it - plus Barry Bolton is apparently using it, so it must be good!

Check the shape of the propodeum in profile. In L. niger the propodeum tends to be a smoothly rounded dome, whilst in L. platythorax it tends to be more conical in shape.

Finally, look at the relative length of the setae on the mesosoma, especially the pronotum. In L. platythorax these setae tend to be distinctly longer. Seifert (2007) gives figures for the length of the longest setae on the pronotum divided by the length of the head as 0.119±0.009 in L. niger and 0.159±0.010 in L. platythorax.

The two species have distinct ecological preferences. L. niger prefers drier habitats and has synanthropic tendencies - this is the species that sometimes invades houses. L. platythorax prefers wetter conditions, and is usually the species found in woodland and wet grasslands.

I've also started noticing that the larvae in L. platythorax seem to be more slender than in L. niger. Of course, this is based wholly on my subjective observations, but might be a good indicative field character.

NB: The photomontages are of British specimens² that show generally typical characteristics. However, both specimens show setae on the propodeum that curve forward, which is not typical. In the Scottish L. platythorax, which were collected in atypical habitat at their most northern known location in the UK, the entire series had curved forward propodeal setae.

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¹ American L. niger are most likely a different species again, as the images I have seen do not have the dense clypeal pubescence of L. niger, but do not appear to be L. platythorax either.
² To be honest, I don't think that them being British matters - if anything I find the characteristics of these species to overlap more in the UK than in mainland Europe. However, I know some British myrmecologists who get funny about such things!

Witness to a birth... sort of

Seven weeks ago (to the day) I found a Lasius queen in a soil claustral cell beneath some moss in a woodland.

I don't make a habit of collecting Lasius queens to rear colonies from - they are two-a-penny in the UK (only slightly more expensive than a-dime-a-dozen at todays exchange rate) and the workers are marvellous escapologists, making them difficult to keep.

However, this queen looked like a Lasius flavus queen, so I thought she might be something more interesting since woodland is not the normal habitat for L. flavus. I collected the queen and the soil of the cell surrounding her and placed everything in a tube.

She had remained in that tube until yesterday, when I decided it was time to investigate why I hadn't seen any activity for about three weeks. Of course, this meant that when I discovered the queen and brood and two callow workers it was too late to get them back in the tube, so I had to find them some alternative accommodation in a plaster nest.

I left them to settle into the plaster nest, checking on them every couple of hours. Then in the early evening I counted not two but three workers, so I decided that I would take them into work today, so that I could keep an eye on them.

I'm glad I did. Not a lot happened until 16:00 when, as I was moving to get a drink, I spotted activity. The queen was licking what was obviously an emerging adult ant. The other workers were also showing an above normal level of excitement (i.e. they were moving, rather than just standing over the brood). The queen continued to lick this fourth worker for about 30 minutes, until she left it, twitching, presumably to harden its cuticle.

This was very exciting for me, as in ten years of studying ants it was something I had never before witnessed. To be fair, I've only been keeping ants for about a year and it's the sort of thing that you need to be in the right place at the right time to see.

Once I got them home, at around about 18:00, there was a fifth ant! They are yellow, so I'm becoming more convinced that they are just the common L. flavus, but they're entertaining me.

Tachinus rufipes a myrmecophile?

I found this rove beetle under a stone in the middle of a Lasius flavus colony. As a potential myrmecophile it was pretty convincing, as it was in a chamber right in the middle of the colony, though at a distance from the ants. I collected it with a few L. flavus and kept it alive with them for a few days before deciding to work out what it is.

I originally thought it might be Lamprinodes saginatus, a species associated with ants, including Lasius. However, I'm not a coleopterist and the Staphylinidae are particularly difficult, so I am indebted to Don from the BWARS forum for suggesting an identity from these pictures and describing a bit about the genus.

Apparently it is most likely a male Tachinus rufipes, a not uncommon species in the UK. Tachinus tend to live in grass tussocks, decaying vegetation, dung, carrion, etc, so seem to be generalists. None are listed in Donisthorpe's The Guests of British Ants (1927) as being myrmecophilous. Whether or not this species should be regarded as a myrmecophile probably depends upon how many other times it's found in ant nests, but it is certainly not a species that is dependent upon ants. Most likely the ants were providing suitable conditions and a possible food source. This relationship may not come without a price to the beetle, as both antennae in this specimen are missing segments at the end.

The site it was collected from is one of my favourites and is usually the first site I visit each year. It is a steep south-facing grassland in a sheltered valley and has a lot of flat stones on the ground under which ants nest. Early in the year whole colonies are easy to find just under these stones, along with their myrmecophiles. It was originally visited by Cedric Collingwood in 1960; I checked it out 40 years later and rediscovered Formica cunicularia. These F. cunicularia all seem to be doing something they shouldn't, as they are polygynous, so this year I collected a colony with five queens to observe. Other species recorded include:

• Myrmica sabuleti
• Myrmica scabrinodis
• Myrmecina graminicola
• Lasius alienus
• Lasius brunneus
• Lasius flavus
• Formica fusca
• Claviger testaceus
• Platyarthrus hoffmannseggi

plus a few as yet unidentified possible myrmecophiles, most of which are more nondescript rove beetles. There aren't that many species of ant in the UK, so any site with eight or more species and frequent myrmecophiles is somewhat exciting.

Unusual petiole shape in Lasius umbratus

In my last post I mentioned photographs of a queen ant that were posted to the BWARS discussion group. I asked the collector to send the specimen so that it could be identified properly and I've now had the opportunity to look at it.

It is a Lasius umbratus queen, which was correctly guessed by Andrew Jarman (my guess wasn't even in the right genus). The L. umbratus group is difficult, so I worked the specimen through a number of keys, but it was the head measurements in Seifert (1988) that gave the least ambiguous answer.

The petiole, the interesting thing about this specimen, is as unusual as it appeared in the original photographs taken by Claes-Göran Magnusson. So as to give a clearer impression I've taken some images of my own. The petiole in L. umbratus usually is emarginate, but it can be seen from these photographs that the emargination is much deeper, almost to the level of the anterior peduncle.