What's Long Green and Sticky?

Callum and I went along to the botanic gardens in Dundee this afternoon. The best bit of the gardens are the glass houses, one of which has tropical plants. I've been there lots of times but never before seen stick insects there. Strangely there were lots of them lying on their backs and looking a bit dead but when we picked them up they were alive so we put them back on the leaves. Almost impossible to get a picture in the glass house because the heat and humidity steams up the camera lens. Sticky is therefore in extras.