In reply to Lesdavmor:
We were there in mid May and did the Las Espadas Traverse camping at the Lake which was snow bound and still totally frozen. We were surprised at the amount of snow there was up there. Foolishly we hadn't taken our crampons up and regretted it. We just about got away with it but had to miss out the start of the ridge as we couldn't get up the snow slope without crampons.
I'm not sure how quickly the snow melts up there I would say you would definitely need an axe and for the small amount of extra weight would say it would be daft not to take crampons.