Speckled Wood feeding on ripe plum

When I took this photo I didn't realise that this Speckled Wood had landed by one of the few over ripe plums left on the tree. This butterfly is rarely seen nectaring on flowers, they feed instead on honeydew, but they appear to be partial to the sweet juice of plums.

Loving the ivy

The late flowers of the ivy are a bug magnet in the autumn, when other sources of nectar are scarce. I have posted before on ivy fest season, but today I came across some new ivy visitors in a large ivy just starting to bloom in my local cemetery. Speckled Wood butterflies rarely visit flowers, as they usually feed on honeydew produced by aphids up in trees. So, I was pleasantly surprised to see two individuals feeding on ivy together with a Comma and many Droneflies.

Speckled Wood and Comma

Comma

Dronefly Eristalis tenax

Male wasp

Helophilus

Yellow dung fly?

Knowledge is power for the sun spot owners

Even as the butterfly season comes to an end, Speckled Wood butterflies, Pararge aegeria, are still going strong in my local overgrown cemetery. The hundred year old trees, shade the ground and sunny clearings are highly prized by Speckled Wood males. Yesterday, I watched them squabbling incessantly in a patch of grassy area amongst the trees. At some point, the resident male chased two other individuals, the three butterflies flying around in tight circles away from the prized spot. Another individual comes by oblivious to the ownership contest and takes possession of a sunny dock leaf in prime position (above). By the time the initial "owner" comes back victorious from the skirmish, the newly arrived one believes this is his spot and the subsequent squabble ensues. It is really never ending in this warm autumnal morning with the sunspot owners.
 What determines how is the fight settled? In the late 1970s Davies work suggested that prior ownership is a very strong predictor of success in a fight: residents always won. Later work by Christer Wiklund and collaborators have expanded and refined Davies' findings, indicating that although a good predictor, ownership is not the only factor involved in territorial fights. Age and size are factors that are known to be predictors of fight outcome, but in the Speckled Wood these have little importance. Martin Bergman, Martin Olofsson and Christer Wiklund investigated the effect of motivation on territorial fight outcome. Residents might be more motivated to fight because they have more information on the value of the resource they are fighting for: the resident male might have prior mating experience in that spot, or knows how prized the spot is for other males. The intruder, most of the time lacks such information. This creates an asymmetry in which the resident is more determined to fight than an intruder.
 To test this hypothesis, the researchers set up experiments in large outdoor cages with a prime large sun-spot, and smaller, suboptimal sunspots. They released two males in each cage and waited until there was a clear dominant male that took possession of the large sunspot. They they removed the dominant male and divided the subordinate males in two groups, half of the males repeatedly encountered a female during a 30 min residency period (female encounter group), while the other half (the control group) did not have any female encounters. Then they tested the effect of this prior experience - motivated vs unmotivated males - on contest outcome when they introduced the original dominant individual back in the cage. The results were very clear.

Outcome of contests between Speckled Wood males during the second contest period when the original winner had been reintroduced, and after the original losers had either interacted with a female during 30 min (female encounter group, n = 30) or been alone for 30 min (control group, n = 30); ‘reversal’ (open bars) denotes that the male that lost the contest during the first contest period reversed the outcome and won the contest against the original winner in the second contest period, and ‘no reversal’ (filled bars) denotes that the same male won in both contest periods (from Bergman et al 2010).

Half of the originally subordinate males won their fight with the original dominant in the "female encounter group". In contrast, most of the dominant males won their fight for the prime sunspot when no females had been present. Also, the fights in the treatment group were more intense and took longer to resolve, while the control group the fights were settled quickly. In conclusion, these experiments showed that male experience in a sun spot increase his persistence in a fight, and therefore increase the chances of winning it, even if he was initially a subordinate male, indicating that motivation is an important factor for contest resolution in the Speckled Wood.

References

Bergman, M., Olofsson, M. & Wiklund, C. (2010). Contest outcome in a territorial butterfly: the role of motivation Proceedings of the Royal Society B: Biological Sciences, 277 (1696), 3027-3033 DOI: 10.1098/rspb.2010.0646
Davies, N. (1978). Territorial defence in the speckled wood butterfly (Pararge aegeria): The resident always wins Animal Behaviour, 26, 138-147 DOI: 10.1016/0003-3472(78)90013-1

September bugs

There is a definite autumnal feel these days. Shorter days, ripening berries and leaves already changing colour. September, however, is a month plentiful on all sorts of bugs. During a walk in our local Millennium Wood, Oppy Wood today, we spotted five butterfly species, Comma, Speckled Wood, Small Tortoiseshell, Red Admiral and Large White. We watched Commas and Speckled Woods sucking the sweet juice of ripe Blackberries.

There were plenty of Daddy Long Legs (tipulidae). Some of them mating.

A couple of Migrant Hawkers patrolled above our heads. A male (top) eventually stopped to rest, hanging from some low branches. He let me get really close to him for some shots.

There also were grasshoppers about - possibly Lesser Marsh Grasshopper, Chorthipphus albomarginatus - 7 spot ladybirds, froghoppers and wolf spiders.

A male Lesser Marsh Grasshopper

The sunspot owners: Speckled Wood butterflies

Male Speckled Wood perched on his sunny spot

The Speckled Wood (Pararge aegeria) butterfly is largely a new millennium butterfly in East Yorkshire. Probably due to the warming climate in the British Isles, the range of this butterfly is gradually increasing north. I saw the first Speckled Wood in Hull in a disused cemetery with large trees and lush undergrowth in 2005. This is a woodland and hedgerow species, not often found feeding on flowers. Adults feed mainly on tree canopies on honeydew, a lovely name for the sugar-laden aphid and scale insect sticky secretions. The most obvious individuals are males, which defend sunlight spots on the woodland floor. They rest on exposed, sunny leaves and inspect any butterfly or insect that passes by. Other butterfly species are briefly checked before the males come back to their resting place, females are courted, and intruding Speckled Wood males that come down from the tree canopy are chased in a brief spiral flight. This territorial behaviour was investigated in a classic paper by Nick Davies in woodland near Oxford. He visited the woodland daily and carried out lots of simple experiments with Speckled Wood individuals marked with colour spots. This way he was able to describe in detail the movements of each individual butterfly. Individual males spent all day in a sunny spot in the woodland floor, fluttering around and perching in it, and following faithfully the sunny spot as it moved though the day on the woodland floor. One of the most interesting findings of this study is that every time an intruder entered a sunny spot, and was involved in a 'spiral flight' with the owner, the intruded ended up retreating to the tree canopy and the resident took its position in the sunny spot. In all the spiral flights observed, over 200, the resident always won regardless of his condition. Davies concluded that the spiral flight is not a 'fight' but a courteous exchange of pleasantries: "to put it anthropomorphically, the owner says 'I was first here and the intruder says 'Sorry, I didn't know there was anybody occupying the sunspot, I'll retreat back to the canopy'. The reason the intruder comes down into the canopy is that it doesn't know the spot is taken. Davies carried out some experiments in which he introduced a male into an already occupied sunspot without the resident male noticing (he remarks he failed frequently, as the resident male seems to be always on the lookout for intruders). In the five occasions he succeeded, the spiral flight escalated and was more lengthy than usual, as both males regarded themselves as the territory owners. Only a few seconds of residency were enough for them to consider themselves the spot owners. Males were competing for the sunny spots and the tree canopy males readily occupied empty spots. The reason for this competition is that females often visit these sunny spots and therefore, males defending a sunspot are more likely to mate. The males on the canopy do not defend a territory but patrol the trees up and down in search of the rarer females. 

Female Speckled Wood

Male perched on his sunny spot