For these pictures you need to use some lateral thinking and have a reasonable general knowledge of entomology – the formal keys are often not much use here! What follows below is an entomological stream of consciousness (eat your heart out James Joyce, or not).
The creature on the water
About the only insect orders that have members that might walk on water are the Hemiptera and the Coleoptera. Coleoptera never overlap their forewings and do not have membranous parts of the forewings. You can just make out that the wings overlap and the tips of the wings might be membranous. Thus it is a Hemiptera. The wings are held flat, and this alone tells us it is sub-order Heteroptera – this is just as well as I know of no aquatic Homoptera! Now we can go to the Heteroptera key in Chinery (Chinery, M (1993, 3rd edition) A Field Guide to the Insects of Britain and Northern Europe. Collins, London):
Q1: antennae visible from above, living on water surface
Q2: head not more than 3 times as long a broad (bit tricky to see, but you can just make it out)
Q3: antennae longer than width of head
Q4: Antennae 5 segmented, or antennae 4 Segmented? No idea! We will have to follow both leads
So if antennae 5 segmented, Q5: bugs over 3mm long, this takes us to Acanthosomatidae, Cynidae, Scutelleridae, or Pentatomidae. These are all largish often shield-bug like terrestrial families. Our bug does not fit this, and so at Q4 it must have 4 segmented antennae
Q10: underside of abdomen densely covered with fine hairs (cannot tell), insects usually living on water surface (yes)
Q11: insects not greenish
Q12: Hind femora reaching beyond tip of abdomen (cannot tell), middle legs inserted nearer to hind ones than to front ones – hard to tell, but looks a bit like this. This makes it a member of the Gerridae, the pondskaters. The alternative here would be the Veliidae. This family only has 2 common species, both of which are rather smaller than this specimen.
The insect on the flower
There are only two orders with stout, hairy, clear-winged adults like this, the Diptera and Hymenoptera. We cannot easily tell if it has two pairs of wings or not, or whether it has halteres, which would easily distinguish between these orders, but the antennae and the mouthparts both tell me this is a Diptera. Hymenoptera never have the strange antennae that this has, and you can just about make out the base of the large labellum that this creature uses to suck fluids up, again unlike in the Hypenoptera.
So, to the Diptera key in Chinery:
Q1 Antennae never long and threadlike
Q20: normal fly without flattened body
Q23 antennae shorter than width of head (the other couplet takes you to a family not in the UK)
Q24: not small and bulbous with a tiny head
Q25: wing-tips not sharply pointed, at least one cross vein near middle of wing
Q25: does not look like a vein running parallel to the hind wing of the insect and forming a false margin
Q28: foot with 3 pads or 2 pads and or claws replacing pads? Pushing our luck a bit here, but I can just make out 2 claws here, and so will go with this one
Q33:Head not abnormally large
Q34: cannot see hind tarsi, but I doubt it is a member of the Platypezidae
Q35: Anal cell? Cannot see this, but it does not look like a member of the families with a long anal cell, and so I will go with the other route, anal cell short blunt or absent
Q40: Frons with a ptilinal suture (curves around the front of the head around the antennae like an upturned U) – just about visible, with some imagination
Q43: this now asks about structures on the thorax and antennae, which cannot be seen at all, and so we can go no further with this key. However, we have got quite a way here. Putting the key to one side, looking at the antennae I would say that it is a member of the sub-order Cyclorrhapa, and it could be a member of the Calliphoridae. However, largish metallic green flies similar to this do occur in other families, some of which have recently been split off from the Calliphoridae.
