Non-Magic, Real-Life Fairies?

Question

Garden Fairies exist...

But not in the way we thought.

A strange form of life borrowing traits from insects and plants with a human-like appearance.

This is a reality-check, is what I am about to suggest at all possible? What improvements need to be made to make it plausible.

Aside: how these fairies evolved to be like they are is not important, as long as their present form is plausible.

The fairies have elongated limbs (rather insectile but four limbs and one trunk/main body part, humanoid face) and large thin wings. This is to increase surface area to volume as they photosynthesise (have chloroplasts). The volume is further decreased by them not being taller than five centimetres. They must roughly conform, especially at a distance, to the general look of a european flower fairy

They do not fly but due to their large wings (butterfly like proportions), small size and hollow bones (fairies are delicate) they can glide. (Mom I saw a tiny flying human in the garden!) I chose for them not to fly because I was worried it would be to energy intensive but it would be a bonus if they could.

To supplement their diet I thought they could, much like aphids, drink plant sap. (Who said fairies love plants?). To do this successfully they would need a stylet like an aphid so maybe like scientists they kill aphids and use the aphid's stylets. Else they could have very thin fingers that can make a small hole which allows sap to gush out.

If they use aphid's stylets, fairies would encounter hard times when aphids are sprayed to death (no more tools, no more sap).

So they would love to sunbathe and would stay around plants.

Answer 1

Acquiring semi-hollow bones requires an intense evolutionary selection process, in combination with size selection(1). the lack of feathers makes the evolution of wings more improbable, but will still have evolved from the ability to glide.

They would not be Tetrapods, as they would have six limbs (wings are limbs). The faeries would be Teleostomi(2), alongside tetrapods and bony fish. So the faeries would be as closely related to us as bony fish are.

This means that a large family of animals exist with six limbs, with varies levels of gliding capability for the middle limbs. These limbs may have evolved alongside the other limbs from different kinds of fins, and might originally have been used as guidance under water rather than thrust.

Note that the fused arch (Synapsid(3)), evolved after the body plan of four legs. So there would need to be a significant amount of convergent evolution between tetrapods and our hexapods.

Note that your faeries may eat algae. The seaslug Elysia chlorotica(4) is able to make proteins necessary for photosynthesis through its ingestion of algae.

The prime marker for intelligence in a species isn't absolute brainsize, but rather relative in size to the body. The crow family consists of incredibly smart birds, magpies are even considered to be self-aware(5). It isn't impossible that the faeries would gain near-human intelligence, their heads would likely be a little larger relative to their bodies than with humans.

It is unlikely that the faeries would have such distinctive noses as we have. We are omnivores, and the faeries wouldn't have one canines or incisors. Humans have excellent vision, whether the same would apply for faeries is doubtful. The level of convergent evolution you're expecting is extremely unlikely.

That said, the high intelligence would likely lead to an ability to adapt tools. For crows this is the beak, for elephants the trunk, for bipedal hexapods, this would mean hands with thumbs.

Answer 2

They're perfectly plausible

There isn't much about your fairies that don't already exist in some other animal, at least in some form. The size is no issue at all: Many actual insects reach or even exceed the 5cm mark, and from the other side there are several mammals and a few birds which are no more than 5cm in length. The main issue would be intelligence, but this isn't much of a problem: Ants and bees are quite intelligent, and have almost all of the traits required for civilisation. Hence your fairies, which are both much larger and much more encephalized, should have more than enough brain space for sapience

Aside from the size, most of their anatomy is just human anatomy, which obviously is plausible. On the wings: If they do not need to fly, then there are pretty much no real issues here. You could have regular leaves appended to the back, with some arteries and veins replacing the standard xylem system and a bit of cartilage or such to add support. These leaves could simply attach to the flesh of the back, with a layer of tougher connective tissue linking them to the backbone and the spine of the scapula.

Photosynthesis also seems plausible enough. Using ants as a model for weight/energy consumption, your fairies would have an average power requirement of 18mW. With butterfly-type proportions, the wings/leaves would have an area of approximately 22cm^2 and will capture at most 1.35W of sunlight. At a 2% photosynthetic efficiency, this will provide a maximum of 27mW during the day. While this is a lot, it is not enough to keep the fairies 'fed' over night (especially given that they'll likely be doing things that are suboptimal for collecting light).

Consuming sap could be a useful way of supplementing their diet. However, fairies are very large compared to other sap-sucking animals, even accounting for their photosynthesis. Coupled with the fact that sap is quite hard to digest, it seems like it would make sense for other food sources, such as nectar or honeydew, to be included in their diet.