Good news! Iris larvae made the most of fine weather during the last 10 days of May to feed up and grow like mad. In N Wilts they shot through the 4th instar and are becoming full grown now - only the weather seems likely to go into Jubilee mode (i.e. wet), which will slow pupation right down, or prevent it altogether. At early sites (Sussex & Surrey) some may have pupated already.
All this means that we are, at this stage, on track for a late June appearance - BUT everything depends on June weather as the insect can go through the pupal period in 2 weeks or get stuck in it for ages, as happened last summer when outdoor pupae were lasting an average of 28 days.
Correction: My thanks to Derek Smith for pointing out that iris hibernates in the 3rd not 4th instar! I have a mental block on this, as I got it into my head aged about 13 that the beast hibernates in the 4th instar - and I periodically lapse back into that mode. Pleased to say that I've got this bit correct in a forthcoming article on iris larvae in the next edition of British Wildlife magazine (entitled Adventures with Caterpillars)... I may eventually grow out of this habitat...
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4 comments:
You also forgot to correct that Derek also noticed that iris only has five larval instar's, not six! The only mention that I am aware of with respect to a putative sixth ilia larval instar was by Ekkehard Friedrich in his "Die Schillerfalter" text, where when comparing head capsule sizes he simply notes one large ilia head capsule as 5? 6?
In 2010 I watched an iris cat (called Nero) go through three skin changes after hibernation - and I have photographs recording all of these. The 1st skin change happened around 9th May. I assumed him to be in 3rd instar. If it is of interest I can post or e-mail the photos to confirm the instar. The 2nd skin change happened around 1st June. The third occurred around 21st June. If he hibernated in 3rd instar that means the last change was into 6th instar. I later believed 'him' to be 'her' (for the silly, romantic reason that an egg was laid on his/her resting leaf - resulting in a caterpillar called Hadrian). Guy
Guy,
Dependent upon larval development (usually late in the season), it is certainly quite normal for iris larvae to diapause in the (late) 2nd not 3rd instar. Do you perhaps have any larval measurements which could help to ascertain if the larvae in question (Nero) was in fact in his/her 2nd or 3rd instar prior to diapause?
I have sent you some pictures, irisscientist. I believe Nero was about 1cm long when I found him in early May but I don't have a formal record of this.
Guy
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