Need some more info please if you can't provide a photo:-

1. Leeches? These usually look a bit like slugs or worms, is that what yours look like? Do you mean caterpillars?

2. Are these things on the leaves, on/in the fruits or on the bark, or all three? Do they move or are they fixed in position?

3. What symptoms are you seeing on the tree otherwise (things such as cracked bark, curling leaves, brown leaves, scarred leaves, orange deposits on leaves, shrivelled fruits, brown mouldy fruits, fruits with holes in them)?

yes everything you said there is right i dont know what to do as we have 2 apple trees too we've had these friut trees 2 yrs now and never had any sign of fruit or blossom

Ugh, nasty - its Pear and Cherry Slug, which is the larvae of a sawfly. Link below gives more information, but the best control is picking the larvae off as soon as you see them and destroying them, before they turn into adult sawflies. Pyrethrum may be effective against them, otherwise insecticidal soap in a spray. You'll need to keep an eye out every year for these, they're difficult to control/get rid of on large trees

http://www.bbc.co.uk/gardening/advice/pests_and_diseases/identifier.shtml?sawflies

Done a bit more research - seems any good contact insecticide will kill them at the slug stage - but that's only any good if your tree is small enough to spray.

And I forgot to say, any insecticide you choose should be suitable for use on edible crops...