Please refer to the following link for further details:
Vellidae = Link 1
Veliidae is a family of predatory insects in the order Hemiptera. They are also known as riffle bugs, smaller water striders or broad-shouldered water striders due to the segment just behind the head being wider than the rest of the abdomen. This differs from the typical water striders (Gerridae), which are close relatives that are also in superfamily Gerrioidea. Unlike some Gerridae, riffle bugs are small and usually about 4.4 mm. long.