It sounds as though you may an infestation of moth, which will be turning into caterpillars any minute now, and before you know it, your pear tree will be stripped of leaves. Those cobweb sacks are nests which the adult moth spins to protect her developing eggs and larvae. I'm have no idea what they would be called in the States, but here the locals call them something like "processional moths" and they are quite poisonous. I am afraid it is too late for a systemic insecticide or repellent, get the strong stuff out and spray your tree very thoroughly before they move onto other trees and attack them, too. Squash every caterpillar you can possibly find and examine every tree in your garden. I had to work very fast and brutally to stop a serious infestation in our orchard last year, or I would have had no trees with any leaves left at all.

Gattina, thank you for your response. I have a pecan tree near the pear. Hopefully, I can prevent it from getting infected.
Thanks again.

We have those here too and the caterpillars are very dangerous to any animals you might have, as they are so poisonous. Take care when you're getting rid of them.

The people round here go on "caterpillar squashing walks". They are called processional moths because they form great long queues to disperse themselves in the countryside, and you can see lines of the little corpses where people have stamped on them as they go along roads and pathways. Any animals, such as cats, dogs or the perennially free-ranging poultry one gets round here will be made extremely ill, and probably die quite horribly should they be foolish enough to eat one. Humans can be affected even by touching them. Do take great care.

Apparently, it's only the front one which can actually see...

I didn't know that! How come he's got sight and the rest haven't?

I can't answer your question, Gattina - but the problem with the pear tree is an infestation of tent caterpillar moths of some variety - some of these are dangerous to humans or animals, having fibres which disperse and irritate the airways, others are toxic. You need to establish precisely which ones you've got before tackling them - here in London, we often get infestations in certain trees of tent caterpillars, and a specialist team is sent out by the Council, masked and suited, to cut the nests out of the trees. Other types of tent caterpillars are harmless, so always best to know what you're dealing with first.

I don't know the answer to that either, Gattina...nature moves in mysterious ways... ;)

thank you all for your help. I think I will contact our parish ag department and let them check it out.

I endorse the safety measures above - be very careful not to go too near - a friend walked beneath a tree where these caterpillars were 'tenting' and accidentally knocked a branch causing a caterpillar to fall down her neck. She was hospitalised for a week! A dog, snuffling around in the grass beneath a 'tented' tree, came into contact with a caterpillar and had to have part of his tongue amputated. These are not sensational horror stories - they are true events. Please be careful.

But, Nariz, as I said, not all tent caterpillars are harmful, there's a limited number - not sure which ones they get in the States though.

Right enough, Bamboo...it's not England... :)

...so, taking advice is the best way, Ghr...Ghrrr!!
Go get 'em! But safely, tho'...!

Yes, I understand that, Bamboo, but who's going to find out whether or not the ones Ghr has on the pear tree are safe or dangerous? I would err on the side of caution and treat them as dangerous unless and until someone can say they are safe.

Yep, too right - I wish I could remember the name of the ones the council used to deal with - I know they were basically brown, striped black and red, with prominent black hairy tufts...

Gosh, Bamboo, that sounds frightfully exotic - ours are small, insignificant pale brown hairy jobbies who pretend to be totally harmless.

...and blind, as well...(apart from the front one)...

Sorry, forgot that bit.......Wearing dark glasses and carrying white canes, too.....