Plodding a regular path near my home, I have been enjoying the emergence of buttercups over the past few weeks. Ever alert to possibility of photographing insects, I have been going around peering into their shiny yellow flowers, to see what I could find. At least I was when the sun was out!
Most buttercups are nectar-producing and are visited by a vast array of different insect species, predominantly bees, flies, wasps and beetles, but many others as well. This tachinid fly (Tachinidae) (below) was quite a common visitor, but I did not feel confident about identifying it. I find these flies difficult to identify! Take a look here.
The numerous stigmata in buttercup flowers (below) cannot all be pollinated by a single visit of one insect, so several visits are needed – by one or more species – to ensure maximal reproductive success for a given flower (Steinbach & Gottsberger, 1994). In short, buttercups must welcome all manner of pollinators.
Insects move quickly and tend to avoid close scrutiny by a large mammal armed with a camera! So some of the insects I saw on buttercups, particularly bees and flies, were unfortunately, not recorded for posterity! However, persistence pays off and I managed to build up a small portfolio of ‘butterfly bedfellows’ over the course of a couple of days. It has to be said that the vast majority of buttercups do not have any insect visitors, at least large ones, at any given time. The game is to look at a lot of flowers! Then, it is fun to try and identify the different species, like this little soldier fly, Microchrysa polita, the black-horned gem (below).
Another insect I came across a few times (below), was a sawfly, Tenthredo arcuata (Tenthredinidae). At first I thought that it was a solitary bee, but some research revealed that it was a sawfly which sometimes predates small insects visiting flowers. There are a few of these sawflies which look very similar when they are covered from head to toe in yellow pollen! However, I think this is the right one, based on appearance and location. There are lots of resources for identifying sawflies, see here. Including a great one, here, prepared by Krisztina Fekete of the Natural History Museum. It takes a few seconds to download.
When I first saw this sawfly (above) it was busy doing whatever it was doing – hunting, gathering pollen? – at about 4:30 pm on a sunny afternoon. Funnily enough, I passed by the same site, still peering into ever buttercup I could find, and I found it again! It might not have been the same individual, but I like to think that it was. This time, it was nicely curled up, and completely stationary in a buttercup flower (below). The time was about 6:20pm and it appeared to have gone to sleep!
Bees and hoverflies (below) like to visit buttercups like meadow buttercup and creeping buttercup (Ranunculus acris and R. repens). There have been concerns that buttercups might be toxic to honey bees as the pollen contains the secondary metabolite ranunculin, a compound which breaks down to release a toxin when the plant is wounded. Although, there are a range of bees which nectar on buttercups, there are specialist buttercup bees (read below).
Unfortunately, one species I did not see on my buttercup visits was the Large scissor bee, also called the Sleepy Carpenter bee, Chelostoma florisomne (below). Probably too far north? These solitary bees (Megachilidae) are pollen-specialist (oligolectic) and are closely associated with the flowers of Ranunculus spp.. Unlike some other, more generalist (polylectic) bees, including honey bees, Chelostoma florisomne bees have a digestive system which can remove and absorb the toxins present in the buttercup pollen (Dobson & Peng, 1997). A diet of pollen from buttercup plants (Ranunculus) can have a deleterious effect on developing larvae of bees which not buttercup specialists (Sedivy et al., 2012). Bees like Chelostoma florisomne have also been observed “curled up around the base of the stamens of buttercups during poor weather, apparently relying on the closure of the petals to shelter them” (BWARS website).
Despite being a more generalist pollinator, the Red mason bee (Osmia bicornis)(see below) is also reportedly able to metabolise Ranunculus pollen (below). I hope I have got the identity of this bee correct! Solitary bees are not easy to identify!😊
Female megachilid bees like this carry pollen on a so-called, scopa, a sort of hairy brush on the ventral side of the abdomen. To collect the pollen, the mason bees brush the anthers and stigmas with their legs and body.
There are specialised hairs on on the scopa (see below), with hooks or branches to trap the pollen grains. Amazingly, researchers have found that these hairs are also electrostatically charged, thus facilitating the electrostatic adhesion of pollen. These hairs collect pollen when brushed over anthers and retain it during flight (Montgomery, 2020). Mason bees are highly efficient pollinators because more pollen is dislodged and transferred between flowers, by means of this electrostatic brushing!
I also came across a parasitised aphid on a buttercup petal (below). There are a number of aphid species which occur on Ranunculus species, perhaps a many as 14 in the UK (Blackman & Eastop, 2006) including some which use the roots or stems of buttercups as secondary plant hosts, i.e. during the summer. Aphids on buttercups include the gall forming poplar/buttercup aphid (Thecabius affinis) and the nice yellow buttercup aphid, Tubaphis ranunculina, which lives on the lower side of the leaves, sometimes moving to the upper side and the stems.
Those aphids that escape being parasitised (above), run the risk of being hoovered up and consumed by a consummate aphid predator: the Seven-spot ladybird – or ladybug if you live in North America – Coccinella 7-punctata (below).
The species which I first went in search of was the Cocksfoot moth (Glyphipterix simpliciella) which I have come across before when photographing buttercups (below). I don’t know much about the biology of this tiny tiny (3 or 4mm long) moth and exactly what it does in buttercups other having a sip of nectar? They also seemed to be flying around a lot, so maybe buttercups are where they meet their friends and would-be lovers! Their larvae feed on other species, especially the grass cocksfoot (Dactylis glomerata).
I have been pleasantly surprised by how many species I managed to capture in a relatively short time. There were lots of little worker bees that I missed, as they tend not to sit still long enough to have their portrait taken! It would have been nice if the weather had stayed sunny for longer, but this is Britain, and the inhabitants, insect and human, have to make the best of it when the sun shines, because they know that rain clouds soon follow!
Blackman, R.L. & Eastop, V.F. (2006). Aphids on the world’s herbaceous plants and shrubs. Vols 1 and 2. John Wiley & Sons.
Dobson, H. E., & Peng, Y. S. (1997). Digestion of pollen components by larvae of the flower-specialist bee Chelostoma florisomne (Hymenoptera: Megachilidae). Journal of Insect Physiology, 43(1), 89-100.
Montgomery, C. M. (2020). The electric ecology of bumblebees (Doctoral dissertation, University of Bristol).
Sedivy, C., Piskorski, R., Müller, A., & Dorn, S. (2012). Too low to kill: concentration of the secondary metabolite ranunculin in buttercup pollen does not affect bee larval survival. Journal of chemical ecology, 38(8), 996-1002.
Vastrad, R. G. (2020). A STUDY OF FLORAL SPECIALIZATION IN SOLITARY BEES. Lulu Publications. Raleigh, USA
Steinbach, K., & Gottsberger, G. (1994). Phenology and pollination biology of five Ranunculus species in Giessen, Central Germany. Phyton, 34(2), 203-218.