Subject: Re: Vision

From: Ron Rutowski <[email-masked]>
Date: Wed, 3 Jul 1996 14:10:12 -0700

At 04:34 PM 7/2/96 +0000, you wrote:
>Could someone educate me as to how far a butterfly can see? I'm curious to know
>how ommatidia improve the vision of the insect and the capabilities of vision.
>
>

Lynette:

As it happens my lab has just begun an attempt to answer your question.  The
answer is, of course, that it depends on what you mean by "see."  We are
beginning our study by asking how far away a moving object can be, and be
detected by a butterfly.  Clearly this distance depends on the size of the
object.  We are using a model flying device to fly butterfly-like objects on
straight flight paths and at butterfly-like speeds near perched males of the
desert hackberry butterfly, Asterocampa leilia.   Males use a sit and wait
tactic to encounter females.   Only the most preliminary results are in but
at this point no male has flown up and chased the model  when the minimum
distance to the model was more than 3 meters.   So, perched male butterflies
can "see" females only if they fly within about 3 meters of the male.

Again, the size of the object matters here.  We have seen males fly after
birds, e.g. mockingbirds,  flying more than 3 m over males.   Speed of the
object, the background against which it is flying,  the body orientation of
the male relative to the objects flight path, etc. will all affect the
distance at which athe object can be seen.  We hope to explore the effects
of some of these variables in our study so that we may better understand why
males perch the way they do at encounter sites.

By the way, two key morphological variables that affect visual system acuity
are the size of the facet lens on each ommatidium and the angle between the
optical axes of adjacent ommatidia, called the interommatidial angle.   Eye
regions of high acuity typically have large facets and small interommatidial
angles.  In butterfly eyes facet size does not vary much, as far as I know,
but interommatidial angles can vary quite a bit and are apparently smallest
in a band around the equator of the head and in the dorso-frontal part of
each eye.

Ron Rutowski

Ronald L. Rutowski                              Phone:  602-965-4369
Professor and Associate Chair                           602-965-6241
Department of Zoology                   FAX:    602-965-2519
Arizona State University                        email:  [email-masked]
Tempe, AZ 85287-1501  USA