They will certainly speed up now David, and yes, a smooth run with sensible weather would certainly be best for development - although to be honest, they seem pretty well capable of dealing with whatever comes their way. Anything too challenging and they just delay development and wait it out.
Quite a week in the woods:
Lily L4 MIA
Billy The Kid L4 MIA
Mr Clean L4 MIA
Tiny Montgomery L4 late
Skinny Moo L4 early
Hollis Brown L4 MIA
Corrina L4 MIA
X1 L5 early (assumed)
X2 L4 early
X4 L4 - late
X5 L4 MIA
X10 L4 MIA
DD 1 L4 early
The majority of those MIA are relatively young L4 larvae and have relocated as a result of competition with moth larvae - primarily Winter Moth and Mottled Umber, but also others and various sawfly species.
This is always a problem, but has been exacerbated this year due the the delayed leafing of the sallows, leading to a mass of hungry mouths competing for every leaf that begins to grow. The severity of the damage depends on the relationship between leafing time, and hatching time of all these species, with late leafing trees apparently unable to out-leaf the demand. Early leafing trees are able to put on enough growth before attack to comfortably cope with the onslaught when it arrives.
![1EB0DDB6-435C-42BD-AB99-DBA1DE4682DF.jpeg (2.82 MiB) Viewed 11551 times X5 forced out. See also Billy The Kid photo from last post](./files/thumb_17917_5a662e62a276dd960cf4dc596071fe2a)
- X5 forced out. See also Billy The Kid photo from last post
Anyway - the frustrating result of all this from our point of view, is that any iris cat caught up in all this will soon find himself unable to remain in his neighbourhood. He is forced out to search for food, and undamaged resting leaves big enough to support his weight and offer him the protection he needs. In my experience, this is not a move that iris caterpillars ‘want’ to take. If ample feeding and resting opportunities are to be found in their original neighbourhoods then they don’t tend to move. Perhaps they may seek a sunnier location, if they are in shade and the weather is cool, but I have observed larvae in heavy shade but otherwise perfect conditions stay put and pupate very close to their hibernation spot. This is all fairly obvious - there has to be a very good reason for a bright green caterpillar to walk for several metres along brown branches that are regularly monitored by birds. Seeking the warmth of the sun could be one if development is very slow, but finding food and something to rest upon in relative safety is certainly a good enough reason when those things are no longer available on the doorstep.
There is also the journey to pupation to consider - very often caterpillars seek better pupation sites higher up the tree, so if this journey has to be taken at some point, then it could be of benefit to take it sooner rather than later, and thereby also benefit from the improved conditions (be they warmth, leaf quality etc) for the remainder of the growth phase.
Of course we can’t know the exact motivation, but in terms of tracking them to pupation, this move is critical. Relocate them after this and the odds of following them all the way improve dramatically.
Skinny Moo also relocated as predicted, but thankfully chose the path that kept her within reach. We are encouraged by Matthew to honour Denys Watkins-Pitchford (‘BB’) and keep alive the tradition of calling ‘Ai! Ai!’ when we discover a caterpillar - that isn’t really me but then neither is the double ‘fuck yeah’ that burst forth when Skinny Moo was relocated - if any dog walker turned and caught sight of me up my ladder at that moment they would have rightly quickened their pace. Blame the preceding several hours of bitter disappointment (loss after loss) and the never ceasing onslaught of American culture. Her situation is such that she may move again as she grows, but hopefully this spot will be suitable for this instar at least....
![8C8B183F-084E-4167-B141-AF9BD2C88BEE.jpeg (1.21 MiB) Viewed 11551 times Skinny Moo](./files/thumb_17917_d93372f69b63ff634f201660a8291f61)
- Skinny Moo
X2 is a beautiful caterpillar but at a height almost impossible to photograph unfortunately. A young L4 with extensive black markings on the underside of her horns that continue right down to her mouth. I think this is a variable characteristic of younger instars (certainly 3 & 4) but doesn’t get mentioned very often - by L5 the black has disappeared. It is probably the most striking difference between L4 and L5, but as the majority of photographs are of head-down (having been thoroughly disturbed) larvae, it is rarely picked up. Of course anyone looking closely or captive rearing will know this difference well.
![926B11DB-36DE-464D-AF4A-CE4139DED954.jpeg (3.25 MiB) Viewed 11551 times X2](./files/thumb_17917_d5abf0910468715c4ddfe33a1707b1e4)
- X2
![299C1014-DE48-4FBF-910D-239E59309F95.jpeg (1.24 MiB) Viewed 11551 times X2](./files/thumb_17917_8081af5e32d498f142e9547b02dc0a16)
- X2
![A1E1D27B-D4AF-461F-B6A7-F63B76E081F2.jpeg (402.9 KiB) Viewed 11551 times X2](./files/thumb_17917_7b9c9d6b3899011a1edfa0d6e0263888)
- X2
Interestingly a tree that has received eggs for the last 3 years, is only just coming into leaf. The egg I found there this year was predated, but had the larva hatched and survived the winter I’d have been interested to see if it could have coped with such a late start. It would only just be getting going now, in late May!
![1BB61F61-AFC9-4B2A-AEA7-1C2A6118EDDB.jpeg (3.41 MiB) Viewed 11551 times Late sallow](./files/thumb_17917_236172b3ed6656edbbb708c3989d6c0e)
- Late sallow
Matthew’s record in his book for the latest he’s seen a wild L4 is May 30th, but he informs me it is actually June 2nd. Either way, several of my L4s will beat that this year - if only I can keep track of them to prove it.
![96367230-8EA0-4F7C-8038-8687E5FF734C.jpeg (2.62 MiB) Viewed 11551 times DD1 reducing shadow](./files/thumb_17917_a3b9ae452d31c914b25035eb5eea3bda)
- DD1 reducing shadow
So a much reduced field, but a few remaining that, if they survive, could stay local enough to give me a chance at finding a pupa. It’s looking less likely this year, but we’re still in the game for now.
![8A74A4E3-45A0-455B-A104-2EE20F626B48.jpeg (3.06 MiB) Viewed 11551 times Tiny Montgomery still waiting for L5](./files/thumb_17917_0d40d753d075c69a5c79f09f1013a619)
- Tiny Montgomery still waiting for L5
![DB03DAC7-0C25-4F14-987D-FCEEBBCB4E4E.jpeg (1.81 MiB) Viewed 11551 times X1 22 days as L4](./files/thumb_17917_9eac488b59cca70eb682f83b12374e37)
- X1 22 days as L4