The Essex Skipper, Thymelicus lineola

The Essex Skipper is a fascinating, if tiny and fairly plain, butterfly to identify precisely, trying to distinguish it from the very similar Small Skipper as it buzzes from point to point around rough clumpy grass.

Description

The Essex Skipper looks almost exactly the same as the Small Skipper, and you generally see a fast flying small orange triangle zipping amongst grasses, or perhaps stopping to take nectar from flowers such as Fleabane, and think "Skipper!". This one is a male Essex Skipper.

Bourneside Meadow, 19 07 2014

Sometimes you get the impression of a slightly bug-eyed butterfly, with its large bulging coal-black eyes. In profile, the chin is receding, sometimes giving a "Winnie-the-Pooh" look. Here you can see that the underside of the hind wing is tan, in contrast to that of the fore-wing, which is orange.

Bourneside Meadow, 19 07 2014

Compared to a Small Skipper, the underside (note) of the tips of the antennae is a jet black as opposed to a muddy orange, the wings are slightly more pointed and in the male the sex-brand line is less pronounced and shorter but more exactly parallel to the wing edge. These are features that are usually only clearly seen upon careful examination close to, for example in a photograph long after the butterfly has actually been seen. The easiest strategy to see the ratio of Essex to Small Skippers on a particular site is to wait until they are roosting just before dusk, when the butterflies are still and the differences can be most easily seen.

Here is a photo showing the jet black of the antenna tips, specifically the undersides:

Bourneside Meadow, 19 07 2014

Here is a photo to demonstrate the male sex brand, discrete in comparison to the Small Skipper, and almost exactly parallel to the wing edge. The sex brand is actually a linear patch of "androconial scales" specialised to release the male sex pheromone over the female!

Bourneside Meadow, 19 07 2014

The Essex Skipper is by no means confined to Essex, and the Small Skipper is certainly not the smallest Skipper, but really, what’s in a name anyway?

Distribution

Colonies of this butterfly vary considerably in size, and it is more of a wanderer than the Small Skipper. It could therefore be found in any number of small patches of grassland within the Parish. It is generally supposed to prefer somewhat drier sites than the Small Skipper. Places I have found it reasonably easily in Hadlow include Bourneside Meadow and the Fairlawne set-aside area beside Carpenters Lane to the west of Steers Place.

This butterfly was originally thought to be confined to coastal salt marshes, where the eggs survive occasional immersion, and the species can exist in very large numbers. This perception is now known to be thoroughly mistaken, and any, usually drier, piece of grassland bigger than half a hectare in the Southeast of the UK may contain a colony, perhaps together with a colony of Small Skippers. Essex Skippers also seem to have done well in terms of distribution and have spread significantly in southern England over the last few decades. It has moved northwards in the east as far as Humberside probably as the climate has warmed, and somewhat westwards in the southwest (still patchy in Devon and Cornwall though), perhaps partly being spread as over-wintering eggs in hay transported by road, particularly in drought or flood years. It has also been seen in Ireland now. This does however rather beg the question of why it didn’t spread before! One possibility is an increase in grassy verges along roads, which act both as good habitat and excellent corridors.

However, despite an increase in geographical range, its population (abundance) in Great Britain does seem to have dropped very substantially over the last few decades. Perhaps grasslands and saltmarshes throughout its range have scrubbed over to some extent or other changes have occurred?

On the larger scale this is a Palaeartic butterfly, with a range from southern Scandinavia through Europe to North Africa and east to Central Asia.


Life cycle

The adults start to fly a few weeks in the year than the Small Skipper, but there is considerable overlap of the two species. Like the Small Skipper, the males are more active, territorial and much more easily seen than the females. 

The caterpillar food-plant is usually clumpy Cocksfoot or Creeping Soft Grass, alive or perhaps dead, but oddly enough usually not the Small Skipper’s favourite, Yorkshire Fog which has slightly looser leaf-rolls around the stem, and which is apparently therefore not to the Essex Skipper’s liking.

The eggs are set in short strings of 4 or 5 within (or on?) the grass culm, yellow when laid, but gradually fade to a pearly translucent white. Unlike the Small Skipper, the caterpillars of the Essex Skipper remain within their small tough eggs for 8 months or so. Their curled up bodies and black heads can just be seen within. The Essex Skipper actually spends most of the year in an egg, from July to April!

When they eventually hatch, the caterpillars bite a small hole to get out of their eggs, but don’t bother to eat the rest of the hard shell, and start eating grass tissue straightaway, leaving v-shaped damage cut-ins on the grass leaves, and creating refuges, rolling the grass leaf around them in the typical Skipper “grass-leaf tube”. The caterpillar stage may be from March through to June, when they form a chrysalis at the base of a grass clump, in which they pupate and metamorphosis for a few weeks, perhaps into July. The caterpillars may be distinguished from those of Small Skipper although their bodies are also greenish,  by having a couple of stripes on their brownish rather than green heads.

Oddities

Long known in Europe, it was only distinguished from the Small Skipper in the UK in the 1890s, and so became a “new species” in Great Britain then.

Nowadays it is a bit of a pest of Timothy Grass in North America, where it is known as the European Skipper. It originally arrived in Ontario in grass packing around a glass shipment, and then spread throughout the Canada/US border states from the one dump where the packing from that one shipment was disposed of! Its spread may have been facilitated by transport of the eggs in hay bales. Any bottleneck genetic effect I wonder?

Predators and parasites 

The imported pest is affected by fungi in Northern America, and so possibly in its home range as well!