Triangle of bumps on insects' heads

[laetoli]

What is the triangle of raised bumps on the top of the heads of bees and flies and perhaps other insects? They look like the heads of rivets, though I expect they have nothing to do with the construction of the creature
Best wishes
Paul

[Wild-Woman]

They are 'ocelli' or simple eyes.

[Jason Green]

Morning Paul,

This part is made up of three round ocellus or 'simple eyes', which are mainly light-sensors. They are each made up of one lens and several sensory cells. The rear two are known as the posterior ocelli (a pair) and the front one, the anterior ocellus. These form a triangle, known as the ocellar triangle. They are thought to work on a similar basis to our in as far as the number of lenses goes, and are differenciated from compound eyes by simply posessing just the one lens. They are present in a lot of orders (classification), but not all species within that order.

It is thought they serve two purposes, to monitor light levels to stabilise flight, and also to detect shadows to help evade predators.

These are often an aid to identification - whether or not they form a perfect triangle, and the angle at which they sit in relation to each other.

Take care,

Jason

[The Woodman]

Good explanation, Jason.

[laetoli]

Thanks for this clear, and to my mind surprising, explanation, Jason.

Originally Posted by Jason Green

It is thought [the ocelli] serve two purposes, to monitor light levels to stabilise flight, and also to detect shadows to help evade predators.Jason

I say surprising because I read that bees have 5 opsins - these are the light sensitive proteins in the eye, which respond to different wavelengths of light. We have a paltry three, which means that bees have a much finer appreciation of colour, including u.v. wavelengths of which we are unaware, than us. Although, I read further that they can't see the colour red but this might be apocryphal.

Additional, they have very many segments in their eyes - more than most other insects - so many that it's often difficult to resolve images of bees' eyes down to the segment level - something which is easily achieved with other insects.

All this means that bees see quite astonishingly well with their two compound eyes, in many respects, much better than we do with our mere two lenses and without the blind spots.

So how come natural selection hasn't eliminated these three primitive light sensors from the top of their heads? Segemented eyes are particularly good at detecting movement, what can these three extra lenses give that the thousands of other lenses miss?

Best wishes,
Paul

[laetoli]

Not that I'm doubting at all what you say, Jason. I hope that wasn't how it came across. It just surprises me that some of the most powerful eyes in the animal kingdom need augmentation.
Best wishes,
Paul

[JRsbugs]

Interesting point Paul..

I found a wiki article which might help explain this..

Opsin evolution: key critters (ecdysozoa - Genomewiki)

That didn't come up.. see the third link on google search (genomewiki)

http://www.google.co.uk/search?q=ops...w=1419&bih=722

Janet

[laetoli]

Wow, Janet, that's tough going but absolutely fascinating.

It's plain that I have become very ignorant and science has moved on apace. I'm now reading that there's strong evidence that the dorsal ocelli in bees can perceive form, which means that bees have developed two separate but different imaging systems. Yet another way in which their vision is superior to ours. In the "use it or lose it" world of natural selection these must be complimentary.

The UV opsins are just as intriging - I'm learning that these aren't just in the ocelli and in the compound eyes but also in several parts of the brain and are used in communication, polarised light detection and in circadian rhythm systems.

Do bees look very different in UV light, the way flowers do? Could that be a simple way of discerning between different species that look all but identical to our limited visual apparatus?

Best wishes,
Astonished of North London

[JRsbugs]

It certainly is tough going Paul! I tried to find out the exact science behind the "ancestral bilateran state 'state' " and could only find close references, but I got what it meant. I haven't read the full article yet, it was too nice outside and there are insects which require their photo to be taken!

I don't know the answer to being able to identify bees by putting them under UV light, I imagine if someone could map each species UV sensors and these could be shown in some way then there could be a possibilty. A lot of maybes and coulds.

I found an article about how bees navigate which is interesting, also how they would see a flower..

Answers.com - Can bees see ultraviolet light

A bees-eye view: How insects see flowers very differently to us | Mail Online

I discovered there has been studies on birds using "Reflectance spectroradiometry and multi-spectral cameras".. so who knows what the possibilities are!

Bristol University | School of Biological Sciences | Exploring the fourth dimension