POISON-FANG AND STILETTO 183 



between the rival bees until one of them is 

 driven off. 



Chalicodoma muraria belongs to the genus 

 Osmia. The male and female are very unlike 

 each other in appearance, and might easily be 

 mistaken for different species. The male insect 

 is much the smaller of the two, and is russet-red 

 in colour, while the female is a beautiful velvety 

 black, with dark violet wings. Like all the 

 Osmiae, the Mason Bees collect pollen on the 

 underside of the abdomen, which is covered with 

 stiff, backward-directed bristles, taking the 

 place of the pollen-collecting hairs with which 

 the legs of most bees are provided. 



The Osmiae show considerable diversity in 

 their nest-building habits ; a small species called 

 Chelostomes make their galleries in old straw; 

 they have very long and notched mandibles, 

 with which they cut into the straw, and after 

 cleaning it thoroughly out the bees make little 

 cells with mortar within the slender tube. The 

 thatched roofs of old country cottages, granaries, 

 and barns are sometimes crowded with the 

 galleries of this hard-working little insect. 



Osmia aurulenta cleans out the dried twigs 

 of brambles to form galleries for her cells. The 

 Horned Bee (Osmia bicornis) is the most common 

 British species, and is easily recognized by the 

 two little horns that project from the front of its 

 head. The female alone is adorned in this way, 

 the male being a much less conspicuous looking 

 insect. The Horned Bee varies her nest-building 

 habits with the locality in which she finds herself; 

 in sandy districts she burrows in banks and cliffs, 



