What do the early stages look like?
When the caterpillars first emerge from their eggs they are a very pale brown colour and about 1.5 mm long. Soon after beginning to feed they turn green with thin white lines running down their bodies. Apart from getting bigger their appearance is largely unchanged until the final (4th and 5th) instars when some of them turn brown. By the time of pupation, they are slug-shaped, 25mm long and eight to nine months old.
What do the caterpillars eat?
The caterpillars eat a range of grasses. The main ones recorded are cock's-foot Dactylis glomerata, bents Agrostis spp., fescues Festuca spp. and meadow-grasses Poa spp.
Flowers they take nectar from
The butterflies will feed on honeydew but also take nectar from many flowers.
Brambles and
ragworts are said to be favourites but
common fleabane,
cuckooflower, devil's-bit scabious, hemp-agrimony,
red clover,
thistles, water mint,
wild privet, and wild thyme are also cited. From my own experience a large patch of marjoram left to flower can attract lots of gatekeepers if you’re lucky enough to have a colony nearby.
How are they doing?
The population appears stable at present. The 2022 State of UK butterflies report shows a 42% decrease in numbers since 1976, but this is almost unchanged from the 2015 version.3.
Other interesting facts
Historically, gatekeepers were not frequently seen in city-centre gardens. However, in recent years, they have been recorded at some urban sites across north-east London and Hampstead Heath and, more recently, on Wimbledon and Mitcham commons. It’s thought that this expansion into urban areas may be due in part to changes in the management of urban parks and cemeteries.4.
References
3. State of UK Butterflies
report
Page written by Judy Skinner, reviewed and compiled by Steve Head